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A glucose responsive insulin (GRI) that responds to changes in blood glucose concentrations has remained an elusive goal. Here we describe the development of glucose cleavable linkers based on hydrazone and thiazolidine structures. We developed linkers with low levels of spontaneous hydrolysis but increased level of hydrolysis with rising concentrations of glucose, which demonstrated their glucose responsiveness in vitro. Lipidated hydrazones and thiazolidines were conjugated to the LysB29 side-chain of HI by pH-controlled acylations providing GRIs with glucose responsiveness confirmed in vitro for thiazolidines. Clamp studies showed increased glucose infusion at hyperglycemic conditions for one GRI indicative of a true glucose response. The glucose responsive cleavable linker in these GRIs allow changes in glucose levels to drive the release of active insulin from a circulating depot. We have demonstrated an unprecedented, chemically responsive linker concept for biopharmaceuticals.

Biological membranes have distinct geometries that confer specific functions. However, the molecular mechanisms underlying the phenomenological geometry/function correlations remain elusive. We studied the effect of membrane geometry on the localization of membrane-bound proteins. Quantitative comparative experiments between the two most abundant cellular membrane geometries, spherical and cylindrical, revealed that geometry regulates the spatial segregation of proteins. The measured geometry-driven segregation reached 50-fold for membranes of the same mean curvature, demonstrating a crucial and hitherto unaccounted contribution by Gaussian curvature. Molecular-field theory calculations elucidated the underlying physical and molecular mechanisms. Our results reveal that distinct membrane geometries have specific physicochemical properties and thus establish a ubiquitous mechanistic foundation for unravelling the conserved correlations between biological function and membrane polymorphism., Cellular organelles display highly conserved morphologies, e.g., cylindrical (tubes) or spherical (vesicles), and here we show that their Gaussian curvature differences can regulate protein recruitment.

Peptide YY3-36 (PYY3-36) is an endogenous ligand of the neuropeptide Y2 receptor (Y2R), on which it acts to reduce food intake. Chemically modified PYY3-36 analogues with extended half-lives are potential therapeutics for the treatment of obesity. Here we show that the common half-life extending strategies PEGylation and lipidation not only control PYY3-36's pharmacokinetics but also affect central aspects of its pharmacodynamics. PEGylation of PYY3-36 inhibited endocytosis by increasing receptor dissociation rates (koff), which reduced arrestin-3 (Arr3) activity. This is the first link between Arr3 recruitment and Y2R residence time. C16-lipidation of PYY3-36 had a negligible impact on Y2R signaling, binding, and endocytosis. In contrast, C18acid-lipidation minimized endocytosis, which indicated a decreased internalization through non-arrestin-related mechanisms. We propose a temporal model that connects the properties and position of the half-life extender with receptor Gi versus Arr3 signaling bias. We believe that this will be important for future design of peptide therapeutics.

Aim Analogues of several gastrointestinal peptide hormones have been developed into effective medicines for treatment of diseases such as type 2 diabetes mellitus (T2DM), obesity and short bowel syndrome (SBS). In this study, we aimed to explore whether the combination of glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) into a potent co-agonist could provide additional benefits compared to existing monotherapies. Methods A short-acting (GUB09-123) and a half-life extended (GUB09-145) GLP-1/GLP-2 co-agonist were generated using solid-phase peptide synthesis and tested for effects on food intake, body weight, glucose homeostasis, and gut proliferation in lean mice and in diabetic db/db mice. Results Sub-chronic administration of GUB09-123 to lean mice significantly reduced food intake, improved glucose tolerance, and increased gut volume, superior to monotherapy with the GLP-2 analogue teduglutide. Chronic administration of GUB09-123 to diabetic mice significantly improved glycemic control and showed persistent effects on gastric emptying, superior to monotherapy with the GLP-1 analogue liraglutide. Due to the short-acting nature of the molecule, no effects on body weight were observed, whereas a marked and robust intestinotrophic effect on mainly the small intestine volume and surface area was obtained. In contrast to GUB09–123, sub-chronic administration of a half-life extended GUB09-145 to lean mice caused marked dose-dependent effects on body weight while maintaining its potent intestinotrophic effect. Conclusion Our data demonstrate that the GLP-1/GLP-2 co-agonists have effects on gut morphometry, showing a marked increase in intestinal volume and mucosal surface area. Furthermore, effects on glucose tolerance and long-term glycemic control are evident. Effects on body weight and gastric emptying are also observed depending on the pharmacokinetic properties of the molecule. We suggest that this novel co-agonistic approach could exemplify a novel concept for treatment of T2DM or SBS.

Bariatric surgery is currently the most effective treatment of obesity, which has spurred an interest in developing pharmaceutical mimetics. It is thought that the marked body weight-lowering effects of bariatric surgery involve stimulated secretion of appetite-regulating gut hormones, including glucagon-like peptide 1. We here report that intestinal expression of secretin is markedly upregulated in a rat model of Roux-en-Y gastric bypass, suggesting an additional role of secretin in the beneficial metabolic effects of Roux-en-Y gastric bypass. We therefore developed novel secretin-based peptide co-agonists and identified a lead compound, GUB06-046, that exhibited potent agonism of both the secretin receptor and glucagon-like peptide 1 receptor. Semi-acute administration of GUB06-046 to lean mice significantly decreased cumulative food intake and improved glucose tolerance. Chronic administration of GUB06-046 to diabetic db/db mice for 8 weeks improved glycemic control, as indicated by a 39% decrease in fasting blood glucose and 1.6% reduction of plasma HbA1c levels. Stereological analysis of db/db mice pancreata revealed a 78% increase in beta-cell mass after GUB06-046 treatment, with no impact on exocrine pancreas mass or pancreatic duct epithelial mass. The data demonstrate beneficial effects of GUB06-046 on appetite regulation, glucose homeostasis, and beta-cell mass in db/db mice, without proliferative effects on the exocrine pancreas and the pancreatic duct epithelium. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Proteins anchored to membranes through covalently linked fatty acids and/or isoprenoid groups play crucial roles in all forms of life. Sorting and trafficking of lipidated proteins has traditionally been discussed in the context of partitioning to membrane domains of different lipid composition. We recently showed that membrane shape/curvature can in itself mediate the recruitment of lipidated proteins. However, exactly how membrane curvature and composition synergize remains largely unexplored. Here we investigated how three critical structural parameters of lipids, namely acyl chain saturation, headgroup size, and acyl chain length, modulate the capacity of membrane curvature to recruit lipidated proteins. As a model system we used the lipidated minimal membrane anchor of the GTPase, N-Ras (tN-Ras). Our data revealed complex synergistic effects, whereby tN-Ras binding was higher on planar DOPC than POPC membranes, but inversely higher on curved POPC than DOPC membranes. This variation in the binding to both planar and curved membranes leads to a net increase in the recruitment by membrane curvature of tN-Ras when reducing the acyl chain saturation state. Additionally, we found increased recruitment by membrane curvature of tN-Ras when substituting PC for PE, and when decreasing acyl chain length from 14 to 12 carbons (DMPC versus DLPC). However, these variations in recruitment ability had different origins, with the headgroup size primarily influencing tN-Ras binding to planar membranes whereas the change in acyl chain length primarily affected binding to curved membranes. Molecular field theory calculations recapitulated these findings and revealed lateral pressure as an underlying biophysical mechanism dictating how curvature and composition synergize to modulate recruitment of lipidated proteins. Our findings suggest that the different compositions of cellular compartments could modulate the potency of membrane curvature to recruit lipidated proteins and thereby synergistically regulate the trafficking and sorting of lipidated proteins.

Noncovalent binding of biopharmaceuticals to human serum albumin protects against enzymatic degradation and renal clearance. Herein, we investigated the effect of mono- or divalent small-molecule albumin binders for half-life extension of peptides. For proof-of-principle, the clinically relevant glucagon-like peptide 1 (GLP-1) was functionalized with diflunisal, indomethacin, or both. In vitro, all GLP-1 analogues had subnanomolar GLP-1 receptor potency. Surface plasmon resonance revealed that both small molecules were able to confer albumin affinity to GLP-1 and indicated that affinity is increased for divalent analogues. In lean mice, the divalent GLP-1 analogues were superior to monovalent analogues with respect to control of glucose homeostasis and suppression of food intake. Importantly, divalent GLP-1 analogues showed efficacy comparable to liraglutide, an antidiabetic GLP-1 analogue that carries a long-chain fatty acid. Finally, pharmacokinetic investigations of a divalent GLP-1 analogue demonstrated a promising gain in circulatory half-life and absorption time compared to its monovalent equivalent.

The targeted spatial organization (sorting) of Gprotein-coupled receptors (GPCRs) is essential for their biological function and often takes place in highly curved membrane compartments such as filopodia, endocytic pits, trafficking vesicles or endosome tubules. However, the influence of geometrical membrane curvature on GPCR sorting remains unknown. Here we used fluorescence imaging to establish a quantitative correlation between membrane curvature and sorting of three prototypic class A GPCRs (the neuropeptide Y receptor Y2, the β1 adrenergic receptor and the β2 adrenergic receptor) in living cells. Fitting of a thermodynamic model to the data enabled us to quantify how sorting is mediated by an energetic drive to match receptor shape and membrane curvature. Curvature-dependent sorting was regulated by ligands in a specific manner. We anticipate that this curvature-dependent biomechanical coupling mechanism contributes to the sorting, trafficking and function of transmembrane proteins in general.

Peptide YY

Achieving the optimal combination of multiple glucose measurements and insulin injections provides a complex daily situation for most insulin-dependent diabetes patients with currently available insulin products. To date, several fast-acting and long-acting insulins have been developed. However, while the pharmacokinetic profiles have been optimized, it has remained an elusive goal for decades to develop a Glucose Responsive Insulin (GRI), which can be responsive to the fluctuations in blood glucose concentrations during the day. Here we present an unprecedented GRI concept. The concept is based on the hydrolysis of a cleavable linker that is covalently bound to insulin. The chemical nature of this central linker is designed to rapidly release active insulin when glucose rises above euglycemia (5 mM), and this release of active insulin will increase with increasing blood glucose concentration. The second element of the concept is an albumin-mediated inactivation of the GRI by lipidation. After injection, the GRI will bind to albumin and circulate as a depot, resulting in a slow release of insulin like seen with other basal insulins such as insulin Detemir. At the linker level, we have tested three concentrations of glucose, and glucose responsiveness was demonstrated by a decrease in reaction time with increasing glucose concentration. Moreover, fully conjugated GRI molecules were tested in 90% pancreatectomized rats, a model of type 1 diabetes, demonstrating significant and long-lasting glucose lowering effect as compared to control. Overall, we have demonstrated the feasibility of providing a GRI approach, which combines the properties of a basal insulin with that of a bolus insulin. With the circulating depot approach the concept also holds a promise for liver preference. Ultimately our approach could provide a safe insulin for the treatment of insulin-dependent diabetes with very low risk of side effects. Disclosure K. Mannerstedt: Employee; Self; Gubra. E. Engholm: Employee; Self; Gubra. N.K. Mishra: Employee; Self; Gubra. M. Lundh: Employee; Self; Gubra. N. Buch-Månson: None. L.N. Fink: Employee; Self; Gubra. Stock/Shareholder; Self; Novo Nordisk A/S. S.L. Pedersen: None. P.J. Pedersen: Employee; Self; Gubra. P. Le-Huu: Employee; Self; Gubra, Novo Nordisk A/S. Employee; Spouse/Partner; Novo Nordisk A/S. J. Lai: Employee; Self; Gubra. K.J. Jensen: Consultant; Self; Gubra. Stock/Shareholder; Self; Gubra. K. Fosgerau: Stock/Shareholder; Self; Gubra.

Amylin and Adrenomedullin both belong to the calcitonin peptide family. While amylin plays an important role in maintaining glucose and energy homeostasis, adrenomedullin is primarily known for its beneficial vasoactive effects. We hypothesize that combining the glucoregulatory and anti-obesity properties of amylin with the cardioprotective effects of adrenomedullin could be an effective treatment strategy to address type 2 diabetes, obesity and cardiovascular diseases in one molecule. Here we report the design and receptor potencies of unimolecular peptide agonists with dual activity at the amylin and adrenomedullin receptors. Using solid-phase peptide synthesis, an array of hybrid peptides was rationally designed by substituting amino acids essential for amylin activity into the native adrenomedullin sequence. The pharmacokinetic profile was optimized by lipidation with a C20 diacid. Functional activities of the analogues were measured using a cAMP accumulation assay in cells overexpressing the human amylin receptor subtype 3 (hAMY3-R) or human adrenomedullin receptor subtype 1 (hAM1-R). All analogues were full agonists on both receptors. hAMY3R potencies were comparable to human native amylin, whereas hAM1-R potencies ranged from equipotent to 100-fold less potent compared to human native adrenomedullin. In summary, we have synthesized novel hybrid amylin-adrenomedullin peptide agonists with dual activity at the hAMY3R and hAM1-R. Ongoing studies address in vivo efficacy and potency of amylin-adrenomedullin dual agonists in rodent models of obesity and diabetes. Disclosure L.S. Dalboege: None. P. Magotti: None. N. Buch-Månson: None. E.M. Bech: None. L.N. Fink: Employee; Self; Gubra. Stock/Shareholder; Self; Novo Nordisk A/S. S.L. Pedersen: None. K. Fosgerau: Stock/Shareholder; Self; Gubra.

Adrenomedullin (ADM) is a vasoactive peptide expressed in several peripheral organs and known primarily for its beneficial vasoactive effects. However, ADM is also known to inhibit insulin secretion, and central administration of ADM has been shown to elicit anorexigenic effects. Here, we investigated if peripheral co-administration of ADM and glucagon-like peptide 1 (GLP-1) could subdue the hypoglycaemic effects of ADM while enhancing its anorectic properties. The effects of mono- and combination therapy of ADM and GLP-1 on appetite regulation and glucose homeostasis were assessed acutely in male NMRI mice for 12 h, while effects on glucose homeostasis were assessed by oral glucose tolerance tests (OGTT). While the monotherapy with GLP-1 and ADM resulted in modest anorexigenic effects, co-administration of the two peptides led to a marked additive reduction in food intake. Moreover, while OGTT-evoked blood glucose-excursions were significantly increased by ADM monotherapy, co-administration of ADM with a lower dose of GLP-1 normalized glucose excursions. In conclusion, we demonstrate additive anorectic effects of ADM and GLP-1, and that GLP-1 co-administration prevents ADM-induced impairment of glucose tolerance, suggesting that ADM could be potential anti-obesity target when combined with GLP-1 agonist therapy.

Novel principles for optimizing the properties of peptide-based drugs are needed in order to leverage their full pharmacological potential. We present the design, synthesis, and evaluation of a library of neoglycolipidated glucagon-like peptide 1 (GLP-1) analogues, which are valuable drug candidates for treatment of type 2 diabetes and obesity. Neoglycolipidation of GLP-1 balanced the lipophilicity, directed formation of soluble oligomers, and mediated albumin binding. Moreover, neoglycolipidation did not compromise bioactivity, as in vitro potency of neoglycolipidated GLP-1 analogues was maintained or even improved compared to native GLP-1. This translated into pronounced in vivo efficacy in terms of both decreased acute food intake and improved glucose homeostasis in mice. Thus, we propose neoglycolipidation as a novel, general method for modulating the properties of therapeutic peptides.

Peptides and proteins constitute a vast pool of excellent drug candidates. Evolution has equipped these molecules with superior drug-like properties such as high specificity and potency. However, native peptides and proteins suffer from an inadequate pharmacokinetic profile, and their outstanding pharmacological potential can only be realized if this issue is addressed during drug development. To overcome this challenge, a variety of half-life extension techniques relying on covalent chemical modification have been developed. These methods include PEGylation, fusion to unstructured polypeptide-based PEG mimetics, conjugation of large polysaccharides, native-like glycosylation, lipidation, fusion to albumin or the Fc domain of IgG, and derivatization with bio-orthogonal moieties that direct self-assembly. This review provides an overview of available conjugation chemistries, biophysical properties, and safety data associated with these concepts. Moreover, the effects of these modifications on peptide and protein pharmacokinetics are demonstrated through key examples.

[Image: see text] Strategies for half-life extension are often required in the design of new biopharmaceuticals. This Viewpoint focuses on chemical moieties that convey protraction by albumin binding or by self-assembly to form larger structures, with GLP-1 and insulin as examples.

It is well-known that Roux-en-Y gastric bypass (RYGB) leads to a rapid remission of type 2 diabetes and a marked and long-term body weight loss, but the molecular mechanisms driving these desirable effects are not fully understood. RYGB results in increased plasma levels of several gut peptidergic hormones with either anorexigenic and/or antidiabetic effects. However, the potent effects of RYGB cannot solely be ascribed to these, and it is therefore likely that additional factors play a role. To gain further insight we have characterized the mRNA expression profile in enteroendocrine cells in the gut at day 9, 22 and 60 following surgery in a RYGB rat model. The enteroendocrine cells were identified by chromogranin-A immunohistochemistry staining, and isolated by laser capture microdissection from five locations covering the full rostrocaudal extent of the gastrointestinal tract. The mRNA expression profiles were analyzed by RNAseq, and bioinformatic analyses were applied to identify known and predicted preprohormones differentially regulated following RYGB. In total 64 putative preprohormones were identified in the secretome of rat enteroendocrine cells, of which 40 were shown to be differentially regulated at one or more time-points post surgery, including several well-known preprohormone genes (GCG, CCK, GHRL, GIP, NMU, SCT, NPY, and VIP). Only six preprohormones were differentially regulated at all time-points (NMU, TAC3, FAM3D, SCT1, SCT and ADM). We present the full mRNA expression profile of the secretome of chromogranin A positive enteroendocrine cells following RYGB surgery in rats. The data provides a region-specific characterization of all preprohormone encoding genes in the rat gut, including 23 not hitherto known. This comprehensive catalogue of gut peptide hormone expression might help our understanding of hormone mediated effects of RYGB on diabetes remission and body weight lowering. Disclosure L. Biehl Rudkjaer: Employee; Self; Gubra. C. Zhang: Employee; Self; Gubra. Stock/Shareholder; Self; Gubra. K. Rigbolt: Employee; Self; Gubra. Stock/Shareholder; Self; Gubra. S.L. Pedersen: None. M. Falkenhahn: None. T. Hübschle: Employee; Self; Sanofi-Aventis Deutschland GmbH. T. Schmidt: None. N. Vrang: Board Member; Self; Gubra. Employee; Self; Gubra. Stock/Shareholder; Self; Gubra. J. Jelsing: Stock/Shareholder; Self; Gubra. Research Support; Self; Sanofi.

Aim To determine whether intestinal expression of guanylate cyclase activator 2A (GUCA2A) and guanylate cyclase activator 2B (GUCA2B) genes is regulated in obese humans following Roux-en-Y gastric bypass (RYGB), and to evaluate the corresponding guanylin (GN) and uroguanylin (UGN) peptides for potentially contributing to the beneficial metabolic effects of RYGB. Methods Enteroendocrine cells were harvested peri- and post-RYGB, and GUCA2A/GUCA2B mRNA expression was compared. GN, UGN and their prohormones (proGN, proUGN) were administered subcutaneously in normal-weight mice to evaluate effects on food intake and glucose regulation. The effect of pro-UGN or UGN overexpression, using adeno-associated virus (AAV) vectors, was assessed in diet-induced obese (DIO) mice. Intracerebroventricular administration of GN and UGN was performed in rats for assessment of putative centrally mediated effects on food intake. GN and UGN, as well as their prohormones, were evaluated for effects on glucose-stimulated insulin secretion (GSIS) in rat pancreatic islets and perfused rat pancreas. Results GUCA2A and GUCA2B mRNA expression was significantly upregulated in enteroendocrine cells after RYGB. Peripheral administration of guanylins or prohormones did not influence food intake, oral glucose tolerance, and GSIS. Central administration of GN and UGN did not affect food intake in rats. Chronic AVV-mediated overexpression of UGN and proUGN had no effect on body weight or glucose homeostasis in DIO mice. Conclusion GN and UGN, as well as their prohormones, do not seem to play a significant role in body weight regulation and glycemic control, suggesting that guanylin-family peptides do not show promise as targets for the treatment of obesity or diabetes.

Neuromedin U (NMU) is a 25 amino acid peptide expressed and secreted in the brain and gastrointestinal tract. Data have shown that peripheral administration of human NMU decreases food intake and body weight and improves glucose tolerance in mice, suggesting that NMU receptors constitute a possible anti-diabetic and anti-obesity drug target. However, the clinical use of native NMU is hampered by a poor pharmacokinetic profile. In the current study, we report in vitro and in vivo data from a series of novel lipidated NMU analogs. In vitro plasma stability studies of native NMU were performed to investigate the proteolytic stability and cleavage sites using LC–MS. Native NMU was found to be rapidly cleaved at the C-terminus between Arg24 and Asn25, followed by cleavage between Arg16 and Gly17. Lipidated NMU analogs were generated using solid-phase peptide synthesis, and in vitro potency was investigated using a human embryonic kidney 293-based inositol phosphate accumulation assay. All lipidated analogs had preserved in vitro activity on both NMU receptors with potency improving as the lipidation site was moved away from the receptor-interacting C-terminal octapeptide segment. In vivo efficacy was assessed in lean mice as reduction in food intake after acute subcutaneous administration of 1, 0.3, 0.1, and 0.03 µmol/kg. These lipidated NMU analogs prolonged the anorectic effect of NMU in a dose-dependent manner. This was likely an effect of improved pharmacokinetic properties because of improved vitro plasma stability. Accordingly, the data demonstrate that lipidated NMU analogs may represent drug candidates for the treatment of obesity. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Protein recruitment to biological membranes is motivated by either highly selective recognition of specific target membrane components or non-specific attraction to general physical properties of the membrane, such as charge, lipid heterogeneity, and curvature. Here we discuss the interaction between lipid-anchored proteins and lipid membranes from a comprehensive examination of how features of the membrane and its lipid constituents, including lipid head-group size, composition, heterogeneity, membrane thickness, degree of unsaturation, and membrane geometry, effect the adsorption ability of the proteins. Of key importance is the strong interconnection among these compositional and morphological elements in mediating the binding of peripheral membrane proteins. As a model protein, we use the dual lipidated (palmitoyl and farnesyl) anchoring motif of the signaling GTPase N-Ras (tN-Ras). We find marked augmentation in tN-Ras adsorption with increasing degree of membrane curvature—a trend that is tightly regulated by the bilayer characteristics mentioned above. Experimental results are fully reproduced by a molecular level theoretical model of the systems under study. Of note, the theory suggests an explicit dependence on the lateral pressure profile of the membrane's hydrophobic region to be the mechanism and cause of variation in protein density with membrane curvature and composition. Relief in the lateral pressure of the bilayer's outer leaf, upon its expansion induced by increasing curvature, reduces the work requirement for lipid-anchor insertion into the membrane. Furthermore, the inherent pressure profile of the hydrophobic channel, at a given curvature, is unique with regard to membrane composition, which allows for fine-tuning of lipidated-protein density.

The N-methylation of backbone amides in synthetic peptides is an important method for improving properties such as bioavailability, stability, as well as structural preferences, and is thus an attractive design strategy. However, the synthesis of N-methylated peptides can be challenging as the nucleophile in the acylation step is a sterically hindered secondary amine. In this study, we have systematically evaluated the use of microwave heating, different coupling conditions and the role of steric effects on coupling yields. First, the coupling reagent providing the highest yields was identified by a series of test N-acylation reactions on a selected peptide sequence. Secondly, a comparison of the coupling temperature, that is, room temperature versus microwave heating, with the optimal coupling reagent was performed. Finally, under the optimal conditions, a comprehensive study employing a set of sterically hindered N-methylated amino acids was conducted. Interestingly, incorporation of Fmoc-Arg(Pbf)-OH proceeded with higher yields at room temperature than at elevated temperature as a result of intramolecular Arg lactam formation, which competes with intermolecular amide bond formation. Fmoc-Arg(Boc)2-OH provided even lower coupling yields, due to the complete formation of the Arg lactam product. Our studies have led to a robust, rapid, easy and high-yielding microwave-assisted method using COMU for the incorporation of Fmoc amino acids into challenging, sterically hindered N-methylated amino acid residues in a peptide sequence without the use of harsh reagents.

It has been hypothesized that amphipathic peptides might bind to membranes prior to activating their cognate receptors, but this has proven difficult to test. The peptide hormone PYY3-36 is believed to perform its appetite-suppressing actions through binding to hypothalamic Y2 receptors. It has been proposed that PYY3-36 via its amphipathic α-helix binds to the plasma membrane prior to receptor docking. Here, our aim was to study the implication of this hypothesis using new analogs of PYY3-36. We first studied membrane binding of PYY3-36. Next, we designed a series of PYY3-36 analogs to increase membrane-binding affinity by substituting the N-terminal segment with a de novo designed α-helical, amphipathic sequence. These 2-helix variants of PYY3-36 were assembled by solid-phase peptide synthesis. Pharmacological studies demonstrated that even though the native peptide sequence was radically changed, highly active Y2 receptor agonists were generated. A potent analog, with a Kd of 4 nM for membranes, was structurally characterized by NMR in the membrane-bound state, which clearly showed that it formed the expected 2-helix. The topology of the peptide-micelle association was studied by paramagnetic relaxation enhancement using a spin label, which confirmed that the hydrophobic residues bound to the membrane. Our studies further support the hypothesis that PYY3-36 associates with the membrane and indicate that this can be used in the design of novel molecules with high receptor binding potency. These observations are likely to be generally important for peptide hormones and biopharmaceutical drugs derived from them. This new 2-helix variant of PYY3-36 will be useful as a tool compound for studying peptide-membrane interactions.

Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues.

Precise microwave heating has emerged as a valuable method to aid solid-phase peptide synthesis (SPPS). New methods and reliable protocols, as well as their embodiment in automated instruments, are required to fully use this potential. Here we describe a new automated robotic instrument for SPPS with microwave heating, report protocols for its reliable use and report the application to the synthesis of long sequences, including the beta-amyloid 1-42 peptide. The instrument is built around a valve-free robot originally developed for parallel peptide synthesis, where the robotic arm transports reagents instead of pumping reagents via valves. This is the first example of an 'X-Y' robotic microwave-assisted synthesizer developed for the assembly of long peptides. Although the instrument maintains its capability for parallel synthesis at room temperature, in this paper, we focus on sequential peptide synthesis with microwave heating. With this valve-free instrument and the protocols developed for its use, fast and efficient syntheses of long and difficult peptide sequences were achieved.

The gut hormone PYY3-36 influences food intake and body weight via interaction with hypothalamic presynaptic Y2 receptors (Y2R). Novel Y2R-selective analogues of PYY3-36 are therefore potential drug candidates for the treatment of obesity. It has been hypothesized that PYY3-36 and possibly also the related PP-fold peptides, NPY and PP, bind to the membrane via their amphipathic alpha-helix prior to receptor interaction. The PYY3-36 amphipathic alpha-helix causes the peptide to associate with the membrane, making it essential for Y receptor potency as it potentially guides the C-terminal pentapeptide into the correct conformation for receptor activation. Based on this hypothesis, the importance of the amphipathic nature of PYY3-36, as well as the ability of amphipathic alpha-helices to interact in solution to form di- and tetramers, we redesigned the peptide architecture by addition of an amphipathic alpha-helix via the Lys 4 side chain of PYY3-36. Two different amphipathic sequences were introduced; first, PYY17-31, the native alpha-helix of PYY, and secondly, its retro counterpart, PYY31-17, which is also predicted to form an alpha-helix. Moreover, several different turn motifs between the branching point and the additional alpha-helix were tested. Several novel peptides with nanomolar Y2R binding affinities, as well as increased Y receptor selectivity, were identified. CD experiments showed the modifications to be well accepted, and an increase in mean ellipticity (ME) signifying an increased degree of alpha-helicity was observed. Receptor binding experiments indicated that the direction of the additional alpha-helix is less important, in contrast to the turn motifs, which greatly affect the Y1R binding and thus determine the Y1R activity. Conversely, the structure-activity relationships from in vivo data showed that the peptide containing the retro-sequence was inactive, even though the binding data demonstrated high affinity and selectivity. This demonstrates that radical redesign of peptide architecture can provide nanomolar binding with improved subtype selectivity and with in vivo efficacy.

The Y2 selective PYY derived peptide PYY3-36 was recently shown to play a role in appetite regulation. Novel PYY3-36 analogs with high selectivity for the Y2 receptor could be potential drug candidates for the treatment of obesity. The C-terminal pentapeptide segment of PYY3-36 is believed to bind to the Y receptors. Tyr-36 is highly conserved across species and only few successful modifications of Tyr-36 have been documented. PYY3-36 analogs were prepared using solid-phase peptide chemistry and tested for binding to the Y1, Y2 and Y4 receptor subtypes by radioligand displacement assay. The Y2 receptor agonists with the best affinity and selectivity were further investigated for activity towards the Y1 and Y2 receptor subtypes. Unexpectedly, modifications of Tyr-36 were well-tolerated, and the analogs of PYY3-36 in which the Tyr-36 hydroxyl group was substituted with a halogen or an amino group were particularly well tolerated and yielded an improved selectivity and approximately equipotent affinity to the Y2 receptor. These modifications could be used to design new potential drug candidates for the treatment of obesity. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.

Neuromedin U (NMU) is a gut-brain peptide, implicated in energy and glucose homeostasis via the peripherally expressed NMU receptor 1 (NMUR1) and the central NMUR2. We investigated the effects of a lipidated NMU analog on gastric emptying (GE), glucose homeostasis and food intake to evaluate the use of a NMU analog as drug candidate for treatment of obesity and diabetes. Finally mRNA expression of NMU and NMUR1 in the gut and NMUR2 in the hypothalamus was investigated using a novel chromogen-based in situ hybridization (ISH) assay. Effects on food intake (6 and 18 h post dosing) were addressed in both mice and rats. The effects on GE and glycaemic control were assessed in mice, immediately after the first dose and after seven days of bidaily (BID) dosing. The lipidated NMU analog exerted robust reductions in GE and food intake in mice and improved glycaemic control when measured immediately after the first dose. No effects were observed after seven days BID. In rats, the analog induced only a minor effect on food intake. NMU mRNA was detected in the enteric nervous system throughout the gut, whereas NMUR1 was confined to the lamina propria. NMUR2 was detected in the paraventricular (PVN) and arcuate nuclei (ARC) in mice, with a reduced expression in ARC in rats. In summary, the anorectic effect of the lipidated NMU is partly mediated by a decrease in gastric emptying which is subject to tachyphylaxis after continuous dosing. Susceptibility to NMU appears to be species specific.

Neuromedin U (NMU) is a 25 amino acid peptide expressed and secreted in the brain and gastrointestinal tract. Data have shown that peripheral administration of human NMU decreases food intake and body weight and improves glucose tolerance in mice, suggesting that NMU receptors constitute a possible anti-diabetic and anti-obesity drug target. However, the clinical use of native NMU is hampered by a poor pharmacokinetic profile. In the current study, we report in vitro and in vivo data from a series of novel lipidated NMU analogs. In vitro plasma stability studies of native NMU were performed to investigate the proteolytic stability and cleavage sites using LC-MS. Native NMU was found to be rapidly cleaved at the C-terminus between Arg(24) and Asn(25) , followed by cleavage between Arg(16) and Gly(17) . Lipidated NMU analogs were generated using solid-phase peptide synthesis, and in vitro potency was investigated using a human embryonic kidney 293-based inositol phosphate accumulation assay. All lipidated analogs had preserved in vitro activity on both NMU receptors with potency improving as the lipidation site was moved away from the receptor-interacting C-terminal octapeptide segment. In vivo efficacy was assessed in lean mice as reduction in food intake after acute subcutaneous administration of 1, 0.3, 0.1, and 0.03 µmol/kg. These lipidated NMU analogs prolonged the anorectic effect of NMU in a dose-dependent manner. This was likely an effect of improved pharmacokinetic properties because of improved vitro plasma stability. Accordingly, the data demonstrate that lipidated NMU analogs may represent drug candidates for the treatment of obesity.

This chapter provides an introduction to and an overview of current instrumentation for solid-phase peptide synthesis (SPPS). Presently, the two most common designs differ in their mode of liquid handling: the first relies on valves and valve blocks for distribution of reagents, while the second uses a robotic platform. They also differ in their mode of mixing the reactants in the reaction vessel, where the former can utilize sparging, 180° rotational shaking, or vortexing, while the latter typically uses vortexing. Valve-based instruments are often single channel (one peptide at a time), but can also be expanded to allow parallel synthesis of up to 12 and even 24 peptides, however, at the price of added complexity. Valve systems often use inert gas for their operation. The X-Y robotic platforms are ideal for parallel synthesis of large numbers of peptides up to 192 and even peptide libraries. However, although less common, the robotic platform is also very suitable for single-channel operation and can also be used for operations under inert gas. Some single-channeled synthesizers are available with UV feedback monitoring of the Fmoc removal which can be useful for some applications. Importantly, single-channel synthesizers can be equipped with fast and precise microwave heating to accelerate the synthesis and to overcome synthetic difficulties. A whole range of synthesizers with different designs are commercially available. The choice of peptide synthesizer will depend on intended application, for example on the type of chemistry, scale, and the number of peptides that are required and so on.

After having successfully synthesized a peptide, it has to be released from the solid support, unless it is being used for on-resin display. The linker and, in some cases, the cleavage mixture determine the C-terminal functionality of the released peptide. In most cases, the peptide is released with concomitant removal of side-chain protecting groups. However, some combinations of linkers and side-chain protecting groups enable a two-stage procedure, either using orthogonal chemistry or graduated labilities. Herein, we describe protocols for the release of peptides from the most commonly used linker types providing a variety of different C-terminal functionalities, including acids, amides, amines, and aldehydes. Moreover, suggestions for determination of peptide purity and for storage conditions are provided.

This chapter provides an introduction to and an overview of current instrumentation for solid-phase peptide synthesis (SPPS). Presently, the two most common designs differ in their mode of liquid handling: the first relies on valves and valve blocks for distribution of reagents, while the second uses a robotic platform. They also differ in their mode of mixing the reactants in the reaction vessel, where the former can utilize sparging, 180° rotational shaking, or vortexing, while the latter typically uses vortexing. Valve-based instruments are often single channel (one peptide at a time), but can also be expanded to allow parallel synthesis of up to 12 and even 24 peptides, however, at the price of added complexity. Valve systems often use inert gas for their operation. The X-Y robotic platforms are ideal for parallel synthesis of large numbers of peptides up to 192 and even peptide libraries. However, although less common, the robotic platform is also very suitable for single-channel operation and can also be used for operations under inert gas. Some single-channeled synthesizers are available with UV feedback monitoring of the Fmoc removal which can be useful for some applications. Importantly, single-channel synthesizers can be equipped with fast and precise microwave heating to accelerate the synthesis and to overcome synthetic difficulties. A whole range of synthesizers with different designs are commercially available. The choice of peptide synthesizer will depend on intended application, for example on the type of chemistry, scale, and the number of peptides that are required and so on.

In vivo studies have reported preferential partitioning of Ras GTPases into ordered lipid-protein membrane domains, a process believed to regulate both cellular signaling and protein trafficking.1 However studies in vitro have failed to quantify a preferential partitioning of full length Ras proteins into the liquid ordered phase2,3 and thus a biophysically validated mechanism for in vivo sorting of Ras is still missing. We recently showed that lipidated proteins localize to highly curved membranes in vitro.4 Here we study both in vitro and in vivo whether recruitment by membrane curvature can sort full length lipid-anchored Ras.We employ a single vesicle fluorescence based assay to quantify in vitro the sorting by membrane curvature of full-length Ras proteins. We demonstrate a more than 50 fold increase in protein density on membranes of high curvature as compared to the density on flat membranes. To test for recruitment by membrane curvature in vivo we utilize hypo-osmotic swelling of cells, which flattens curved membrane regions. By measuring the local protein density using FRET,5 we detect a significant reduction in the clustering of Ras and other lipidated proteins upon membrane flattening. This demonstrates that recruitment by membrane curvature can sort Ras and potentially other lipidated proteins in cellular membranes. Furthermore sorting by membrane curvature constitutes the first biophysical sorting mechanism for Ras validated by both in vitro and in vivo measurements.1 Hancock, J. F. Nat. Rev. Mol. Cell Biol.4 (2003).2 Johnson, S. A. et al.Biochim. Biophys. Acta - Biomembranes1798 (2010).3 Nicolini, C. et al.J. Am. Chem. Soc.128 (2006).4 Hatzakis, N. S. et al.Nat. Chem. Biol.5 (2009).5 Kohnke, M. et al.Chem. Biol.19 (2012).

After having successfully synthesized a peptide, it has to be released from the solid support, unless it is being used for on-resin display. The linker and, in some cases, the cleavage mixture determine the C-terminal functionality of the released peptide. In most cases, the peptide is released with concomitant removal of side-chain protecting groups. However, some combinations of linkers and side-chain protecting groups enable a two-stage procedure, either using orthogonal chemistry or graduated labilities. Herein, we describe protocols for the release of peptides from the most commonly used linker types providing a variety of different C-terminal functionalities, including acids, amides, amines, and aldehydes. Moreover, suggestions for determination of peptide purity and for storage conditions are provided.

Precise microwave heating has changed the way many small molecules are being synthesized and, currently, the field of solid-phase peptide synthesis is undergoing dramatic changes owing to the use of microwave heating. To fully reap the benefits of precise microwave heating for the formation of amide bonds in peptide synthesis, it is important to understand the kinetics of formation and break-down of activated esters and their N-acylation of the nascent peptide chain at elevated temperatures. Herein, we present systematic studies of, first, the rate of formation of activated esters by NMR spectroscopy and, second, their N-acylation during peptide synthesis. A study of the amount of residual water in the solvents revealed a significant effect on electrophilic reagents and intermediates. This observation was expanded into a general study of microwave heating in peptide synthesis.

The prevalence of obesity is increasing with an alarming rate worldwide and there is a need for efficacious satiety drugs. PYY3-36 has been shown to play a role in hypothalamic appetite regulation and novel analogs targeting the Y2 receptor have potential as drugs for the treatment of obesity. We have designed a series of novel PYY3-36 isoforms, by first adding the dipeptide Ile-Lys N-terminal to the N(α) of Ser-13 in PYY13-36 and then anchoring the N-terminal segment, e.g. PYY3-12, to the new Lys N(e)-amine. We hypothesized that such modifications would alter the folding of PYY, due to changes in the turn motif, which could change the binding mode to the Y receptor sub-types and possibly also alter metabolic stability. In structure-affinity/activity relationship experiments, one series of PYY isoforms displayed equipotency towards the Y receptors. However, an increased Y2 receptor potency for the second series of PYY isoforms resulted in enhanced Y receptor selectivity compared to PYY3-36. Additionally, acute as well as chronic mice studies showed body-weight-lowering effects for one of the PYY isoforms, which was also reflected in a reduction of circulating leptin levels. Interestingly, while the stability and pharmacokinetic profile of PYY3-36 and the N-terminally modified PYY3-36 analogue were identical, only mice treated with the branched analogue showed marked increases in adiponectin levels as well as reductions in non-esterified free fatty acids and triglycerides.

Precise microwave heating has emerged as a valuable method to aid solid-phase peptide synthesis (SPPS). New methods and reliable protocols, as well as their embodiment in automated instruments, are required to fully use this potential. Here we describe a new automated robotic instrument for SPPS with microwave heating, report protocols for its reliable use and report the application to the synthesis of long sequences, including the beta-amyloid 1-42 peptide. The instrument is built around a valve-free robot originally developed for parallel peptide synthesis, where the robotic arm transports reagents instead of pumping reagents via valves. This is the first example of an 'X-Y' robotic microwave-assisted synthesizer developed for the assembly of long peptides. Although the instrument maintains its capability for parallel synthesis at room temperature, in this paper, we focus on sequential peptide synthesis with microwave heating. With this valve-free instrument and the protocols developed for its use, fast and efficient syntheses of long and difficult peptide sequences were achieved.

Precise microwave heating has emerged as a valuable addition to solid-phase peptide synthesis. New methods and protocols are required to utilize this potential and make it a reliable technique. Here, we describe a new semi-automated instrument for solid-phase peptide synthesis with microwave heating and report protocols for its reliable use. The instrument features a flow-through reaction vessel that is placed in the microwave instrument throughout the synthesis. Bubbling with N 2 gas during the microwave irradiation proved important for temperature control. Washing and Fmoc removal steps were automated, while activated Fmoc-amino acids were added manually. Several linkers and resins were evaluated and protocols for synthesis of difficult sequences were developed. These included on-resin reductive amination of BAL handles under microwave heating. We believe that the instrument, as well as the protocols for its use, will be useful tools for peptide chemists.

The increasing prevalence of obesity worldwide calls for safe and highly efficacious satiety drugs. PYY3-36 has been implicated in food intake regulation, and novel peptide analogues with high Y2 receptor-subtype selectivity and potency have potential as drugs for the treatment of obesity. It has been hypothesized that PYY3-36 associates with the plasma membrane prior to receptor activation such that the amphipathic alpha-helix of PYY3-36 possibly guides the C-terminal pentapeptide into the correct conformation for receptor activation. Ala-scans are used routinely to study the effect of individual amino acids in a given peptide sequence. Here we report the glyco-scan of the peptide hormone PYY3-36, in which hydroxyl side-chain functionalities were glycosylated; in addition new glycosylation sites were introduced. An array of novel PYY3-36 analogues with a glycan positioned in the water-membrane interface or in the N terminal were screened for Y-receptor affinity and selectivity as well as metabolic stability. Interestingly, in contrast to the Y1 and Y4 receptors, the Y2 receptor readily accommodated glycosylations. Especially glycosylations in the alpha-helical region of PYY3-36 were favorable both in terms of Y-receptor selectivity and endopeptidase resistance. We thus report several PYY3-36 analogues with enhanced Y-receptor selectivity. Our results can be used in the design of novel PYY analogues for the treatment of obesity. The glyco-scan concept, as systematically demonstrated here, has the potential for a wider applicability.

The syntheses of two nucleosides with additional nucleobases in the 2′-position are presented. The nucleosides have two- and one-carbon linkers to the additional nucleobase, respectively. The two nucleosides are synthesized from different strategies. The nucleoside with two carbons in the linker has been incorporated into oligonucleotides and showed stabilization of a tree-way junction.

To facilitate the study of the regulation of the rpsA gene, a translational fusion between the rpsA gene and the 1acZ gene was constructed. Synthesis of the fusion protein was repressed about lo-fold when rpsA was supplied in trans on a multicopy plasmid. This repression is similar to the post-transcriptional regulation previously found for the wild type rpsA gene. Addition of purified protein Sl to a coupled in vitro transcription-translation system caused a specific reduction in the synthesis of the rpsA-1acZ fusion protein. Addition of various subdomain fragments of protein Sl to the coupled in vitro system showed that the Nterminal fragment, possessing the ribosome binding domain of protein S 1, was able to repress the synthesis of the rpsA-1acZ fusion protein. In contrast, fragments from the C-terminal region, containing the nucleic acid binding domain of protein Sl, were inactive in this repression. Induction of truncated rpsA genes, coding for either the N-terminal 101 or 329 amino acids caused a reduction in the synthesis of the chromosomally encoded protein Sl, thus confirming in viva that the N-terminal part of protein Sl represses rpsA expression.

The syntheses of two nucleosides with additional nucleobases in the 2′-position are presented. The nucleosides have two- and one-carbon linkers to the additional nucleobase, respectively. The two nucleosides are synthesized from different strategies. The nucleoside with two carbons in the linker has been incorporated into oligonucleotides and showed stabilization of a tree-way junction.

A 5'-C-allylthymidine derivative was prepared from thymidine by the application of a stereoselective allylation procedure and its 5'(S)-configuration was confirmed. From this nucleoside derivative, appropriately protected building blocks were prepared and coupled using standard phosphoramidite chemistry to afford a dinucleotide with two 5'-C-allylgroups. This molecule was used as a substrate for a ring-closing metathesis (RCM) reaction and after deprotection, a 1 : 1 mixture of E- and Z-isomers of a cyclic dinucleotide with an unsaturated 5'-C-to-5'-C connection was obtained. Alternatively, a hydrogenation of the double bond and deprotection afforded a saturated cyclic dinucleotide. An advanced NMR-examination confirmed the constitution of this molecule and indicated a restriction in its overall conformational freedom. After variation of the protecting group strategy, a phosphoramidite building block of the saturated cyclic dinucleotide with the 5'-O-position protected as a pixyl ether and the phosphate protected as a methyl phosphotriester was obtained. This building block was used in the preparation of two 14-mer oligonucleotides with a central artificial bend due to the cyclic dinucleotide moiety. These were found to destabilise duplexes, slightly destabilise bulged duplexes but, to some extent, stabilise a three-way junction in high Mg(2+)-concentrations.

A nucleoside with two nucleobases is incorporated into oligonucleotides. The synthetic building block, 2′-deoxy-2′-C-(2-(thymine-1-yl)ethyl)uridine, 2, is prepared from uridine via 5′,3′-TIPDS-protected 2′-deoxy-2′-C-allyluridine by an oxidative cleavage of the allyl group, a Mitsunobu reaction for the introduction of thymine and appropriate deprotection reactions. This compound is converted into a DMT-protected phosphoramidite and incorporated once into a 13-mer oligodeoxynucleotide sequence, once in an isosequential LNA-modified oligodeoxynucleotide and four times in the middle of a 12-mer oligodeoxynucleotide. These sequences are mixed with different complementary DNA and RNA sequences in order to study the effect of the additional nucleobase in duplexes, in bulged duplexes and in three-way junctions. The first additional thymine is found to be well-accommodated in a DNA–RNA duplex, whereas a DNA–DNA duplex was slightly destabilised. A three-way junction with the additional thymine in the branching point is found to be stabilised in both a DNA–DNA and a DNA–RNA context but destabilised where the modified LNA-sequence is used. In a Mg2+-containing buffer, however, the relative stability of the three-way junctions is found to be opposite with especially the LNA-modified DNA–DNA complex being significantly stabilised by the additional nucleobase.

Sorting and trafficking of membrane-anchored Ras GTPases is critical for signaling and is believed to rely on their preferential portioning in ordered lipid-protein membrane domains (1). However studies in vitro have failed to quantify the preferential partitioning of full length Ras proteins into the liquid ordered phase(2), indicating that a physical principle underlying sorting of Ras is missing. We recently showed that lipidated proteins localize to highly curved membranes in vitro(3, 4). Here we provide a mechanistic insight on how membrane curvature can drive N-Ras sorting.Combining the results of our in vitro assays, measurements on single vesicles, with in vivo studies, hypo-osmotic swelling of cells that flattens curved membrane regions, revealed that : a) N-Ras is preferentially recruited in areas of high membrane curvature and b) membrane curvature is the enabling factor underlying the selective partitioning of NRas in ordered domains. The combined readout of mean field theory calculations and coarse grain simulations provided a mechanistic insight on preferential partitioning in highly curved areas, via the changes in lateral pressure of the outer monolayer when curving an ordered versus a disordered membrane. In addition to providing the first biophysical sorting mechanism for Ras validated by both in vitro and in vivo measurements, our data indicate that membrane curvature may act as a generic cue underlying trafficking and sorting of multiple lipidated proteins.References1. J. F. Hancock, Nat. Rev. Mol. Cell Biol. 4, 373 (2003).2. S. A. Johnson Biochim. Biophys. Acta - Biomembranes 1798, 1427 (2010).3. N. S. Hatzakis et al., Nat. Chem. Biol. 5, 835 (2009).4. V. K. Bhatia, et al Semin. Cell Dev. Biol. 21, 381 (2010).

Cellular membranes define cell boundaries and provide active means for proteins transport and compartmentalization to certain organelles. The prevailing mechanism underlying lipidated protein transport and sorting is based on their selective upconcentration in transient membrane domains of altered fluidity, termed “raft domains”. However the majority of biophysical studies have failed to report increased partition to the lo phase1. We recently illustrated that the farnesylated Gβγ subunit of G protein upconcentrates in highly curved areas and introduced the notion that membrane remodeling may act as a cue for regulating lipidated protein cellular distribution2.Here we capitalized on our developed nanorrays of surface tethered liposomes to quantify the precise effect of membrane curvature and domain formation on the redistribution of the abundant class of signaling proteins, the Ras2-4. Our results demonstrate for the first time that NRas proteins upconcentrate in highly curved areas showing ∼10 fold increased densities as compared to flat bilayers. We furthermore found that NRas does not selectively bind in flat raft domains as compared to ld phases. When however the lo “raft domains” where combined with high curvature a remarkable upconcentration ∼80 fold was documented in the highly curved areas. These findings indicate that lo domains enhance the intrinsic ability of membranes to promote lateral organization of lipidated proteins in highly curved areas.References1. Silvious JR., Biochim. Biophys. Acta, 1610, 174 (2003).2. Hatzakis, N.S. et al. How Curved Membranes Recognize Amphipathic Helices and Protein Anchoring Motifs. Nat. Chem. Biol. 5, 835 (2009).3. Christensen, S., Bolinger P-Y., Hatzakis NS., Stamou D., Nat Nanotech (2011) In Press.4. Larsen K J, Hatzakis N S. Stamou D., J Amer Chem Soc 2011, 133, 10685.

The shape of biological membranes (membrane curvature) has been recognized to regulate the binding and thus the spatial localization of soluble proteins containing BAR domains, amphipathic helices or lipid anchors1-3. However, with few exceptions4,5, the overwhelming majority of the experiments that have validated quantitatively sensing of membrane curvature have been performed with model reconstituted systems in vitro6-10, and thus strictly speaking remain inconclusive regarding the biological relevance of these measurements. Here I will discuss unpublished data on two new assays that allow quantitative characterization of membrane curvature in live cells. We exploited these assays to investigate the influence of membrane shape on the localization of transmembrane G protein coupled receptors and the three major isoforms of Ras (K-, N-, H-).Selected References(1) Madsen, K. L.; Bhatia, V. K.; Gether, U.; Stamou, D. FEBS Letters 2010, 584, 1848.(2) Baumgart, T.; Capraro, B. R.; Zhu, C.; Das, S. L. Annu. Rev. Phys. Chem. 2011, 62, 483.(3) Antonny, B. Annu. Rev. Biochem. 2011, 80, 101.(4) Ramamurthi, K. S.; Lecuyer, S.; Stone, H. A.; Losick, R. Science 2009, 323, 1354.(5) Galic, M. et al. Nat. Cell Biol. 2012, 14, 874.(6) Peter, B.; Kent, H.; Mills, I.; Vallis, Y.; Butler, P.; Evans, P.; McMahon, H. Science 2004, 303, 495.(7) Bigay, J.; Gounon, P.; Robineau, S.; Antonny, B. Nature 2003, 426, 563.(8) Tian, A.; Baumgart, T. Biophysical Journal 2009, 96, 2676.(9) Sorre, B.; Callan-Jones, A.; Manzi, J.; Goud, B.; Prost, J.; Bassereau, P.; Roux, A. Proceedings of the National Academy of Sciences 2012, 109, 173.(10) Hatzakis, N. S.; Bhatia, V. K.; Larsen, J.; Madsen, K. L.; Bolinger, P.-Y.; Kunding, A. H.; Castillo, J.; Gether, U.; Hedegard, P.; Stamou, D. Nat. Chem. Biol. 2009, 5, 835.

Ras proteins are small GTPases that are post-translationally modified by the attachment of lipid moieties (1). This modification is essential for the correct trafficking and sorting of Ras proteins through the vesicular pathway from the Golgi to the plasma membrane (2).Traditionally the sorting of Ras is primarily discussed in the context of membrane domains in flat membranes, neglecting the influence of membrane shape. Recently we have demonstrated, utilizing our single liposome curvature (SLiC) assay that the minimal anchoring motif of N-Ras (tN-Ras) up-concentrates in areas of high membrane curvature (not published), suggesting that curvature might act as a cue for the spatial localization of Ras proteins.In the SLiC assay, curvature-sensing molecules are added from aqueous solution to vesicles of different curvatures, but the vesicles are not in diffusive contact (3, 4). In vivo Ras proteins are anchored to membranes and laterally sorts between curved and planar membranes, which are in diffusive contact. To study the curvature-sensing ability of tN-Ras in a setup mimicking the in vivo scenario we developed a membrane tube based assay in which the tubes are in diffusive contact with a lipid bilayer.Membrane tubes are formed by heating a confined lipid bilayer (5). The tubes eventually adsorb to the flat membrane, which enable imaging by confocal fluorescence microscopy. After addition of tN-Ras we observed a preferential sorting into curved tubes rather than the flat bilayer. This observation further implies a pivoting role of membrane shape as a regulator of Ras-protein localization.1. Prior & Hancock, Semin Cell Dev Biol 23:145(2012).2. Choy et al., Cell 98:69(1999).3. Kunding et al., Biophysical Journal 95:1176(2008).4. Hatzakis et al., Nat Chem Biol 5:835(2009).5. Weirich & Fygenson, Poster Abstract 2731, Biophys. Soc. 2011.