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Magainins are positively charged amphiphatic peptides which permeabilize cell membranes and exhibit antimicrobial activity. Research was conducted which showed that binding of magainins to neutral membranes, a reaction which is difficult to evaluate by spectroscopy, can be followed with high precision using isothermal titration calorimetry. The binding mechanism can be described by a surface partition equilibrium after correcting for electrostatic repulsion by means of the Gouy-Chapman theory.

Helixinduktion: Die synthetische tricyclische Aminosäure ProM ‐ 5, die formal durch stereoselektive Einführung einer Vinylidenbrücke in eine Diprolineinheit entsteht, ist ein leistungsstarkes Gerüst für die Nukleierung der α ‐ Helix ‐ Bildung in einer linearen Peptidkette. Dieses Verhalten könnte bei der Entwicklung neuer Proteomimetika zur Modulation von Proteinwechselwirkungen genutzt werden. [ABSTRACT FROM AUTHOR]

Following ectodomain shedding by p-secretase, successive proteolytic cleavages within the transmembrane sequence (TMS) of the amyloid precursor protein (APP) catalyzed by y-secretase result in the release of amyloid-β3 (A13) peptides of variable length. Aβ peptides with 42 amino acids appear to be the key pathogenic species in Alzheimer's disease, as they are believed to initiate neuronal degeneration. Sulindac sulfide, which is known as a potent y-secretase modulator (GSM), selectively reduces Aβ342 production in favor of shorter Aβ species, such as Ap38. By studying APP-TMS dimerization we previously showed that an attenuated interaction similarly decreased Aβ42 levels and concomitantly increased Aβ38 levels. However, the precise molecular mechanism by which GSMs modulate Aβ production is still unclear. In this study, using a reporter gene-based dimerization assay, we found that APP-TMS dimers are destabilized by sulindac sulfide and related A1342-lowering compounds in a concentration-dependent manner. By surface plasmon resonance analysis and NMR spectroscopy, we show that sulindac sulfide and novel sulindac-derived compounds directly bind to the A13 sequence. Strikingly, the attenuated APP-TMS inter- action by GSM5 correlated strongly with AI342-lowering activity and binding strength to the Aβ sequence. Molecular docking analyses suggest that certain GSMs bind to the GxxxG dimerization motif in the APP-TMS. We conclude that these GSMs decrease Aβ42 levels by modulating APP-TMS interactions. This effect specifically emphasizes the importance of the dimeric APP-TMS as a promising drug target in Alzheimer's disease. [ABSTRACT FROM AUTHOR]

The molecular basis for recognition of peptide ligands endothelin-1, -2 and -3 in endothelin receptors is poorly understood. Especially the origin of ligand selectivity for ETA or ETB is not clearly resolved. We derived sequence-structure-function relationships of peptides and receptors from mutational data and homology modeling. Our major findings are the dissection of peptide ligands into four epitopes and the delineation of four complementary structural portions on receptor side explaining ligand recognition in both endothelin receptor subtypes. In addition, structural determinants for ligand selectivity could be described. As a result, we could improve the selectivity of BQ3020 about 10-fold by a single amino acid substitution, validating our hypothesis for ligand selectivity caused by different entrances to the receptors' transmembrane binding sites. A narrow tunnel shape in ETA is restrictive for a selected group of peptide ligands' N-termini, whereas a broad funnel-shaped entrance in ETB accepts a variety of different shapes and properties of ligands. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The aggregation of the amyloid-β (Aβ) peptide plays a pivotal role in the pathogenesis of Alzheimer's disease, as soluble oligomers are intimately linked to neuronal toxicity and inhibition of hippocampal long-term potentiation (LTP). In the C-terminal region of Aβ there are three consecutive GxxxG dimerization motifs, which we could previously demonstrate to play a critical role in the generation of Aβ. Here, we show that glycine 33 (G33) of the central GxxxG interaction motif within the hydrophobic Aβ sequence is important for the aggregation dynamics of the peptide. Aβ peptides with alanine or isoleucine substitutions of G33 displayed an increased propensity to form higher oligomers, which we could attribute to conformational changes. Importantly, the oligomers of G33 variants were much less toxic than Aβ42 wild type (WT), in vitro and in vivo. Also, whereas Aβ42 WT is known to inhibit LTP, Aβ42 G33 variants had lost the potential to inhibit LTP. Our findings reveal that conformational changes induced by G33 substitutions unlink toxicity and oligomerization of Aβ on the molecular level and suggest that G33 is the key amino acid in the toxic activity of Aβ. Thus, a specific toxic conformation of Aβ exists, which represents a promising target for therapeutic interventions. [ABSTRACT FROM AUTHOR]

A promising application of the depsipeptide technique has recently been proposed to provide ideal conditions for segment condensation, in that coupling of peptides bearing a C-terminal depsipeptide unit occurs without giving rise to epimerization at the activated amino acid. This is due to the low tendency of the activated depsipeptide units, in contrast to the corresponding peptide segments, to form optically labile oxazolones. In this work we demonstrate that coupling of depsipeptides via base-assisted activation using HBTU occurs not only without loss of configuration, but even much faster than the coupling of the corresponding all-amide segments. Nevertheless, when the coupling of long depsipeptide segments proceeds slowly, we uncovered the occurrence of β-elimination at the activated depsipeptide unit, in an extent dependent on the presence of base in the system and on the type of the solvent. Beta-elimination was completely suppressed by using carbodiimide/HOBt activation in a non-polar solvent (DCM), and in more polar media it was limited by substituting TMP for DIEA during HBTU activation, or using particular solvent mixtures (such as DMSO/toluene) for activation via carbodiimide. Finally, we show the application of C-terminal pseudoprolines, in comparison with that of depsipeptide units, to segment coupling. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Human endothelin-1 (ET-1) is a potent vasocontractile 21-residue peptide hormone with significant pharmacological importance. An efficient and straightforward expression strategy that enables cost-effective incorporation of stable isotopes is not available thus far. In this report, we describe a cost-effective expression system in Escherichia coli for the production of ET-1 enriched with 15N and 13C isotopes. Employing thioredoxin as carrier protein, specific and nearly quantitative cleavage of ET-1 from the fusion was mediated by Factor Xa, and purification to homogeneity (final purity of >95%) was achieved by RP-HPLC. Purified recombinant ET-1 was found to be indistinguishable from the synthetic counterpart as determined by mass spectrometry and NMR spectroscopy. Our expression strategy offers the potential for production of isotopically labeled ET-1 in large (mg) quantities for the purpose of heteronuclear NMR experiments. Moreover, the method devised should be applicable for recombinant expression of small peptides in general. [Copyright &y& Elsevier]

The events that occur during chemotaxis of sperm are only partly known. As an essential step toward determining the underlying mechanism, we have recorded Ca2+ dynamics in swimming sperm of marine invertebrates. Stimulation of the sea urchin Arbacia punctulata by the chemoattractant or by intracellular cGMP evokes Ca2+ spikes in the flagellum. A Ca2+ spike elicits a turn in the trajectory followed by a period of straight swimming (‘turn-and-run’). The train of Ca2+ spikes gives rise to repetitive loop-like movements. When sperm swim in a concentration gradient of the attractant, the Ca2+ spikes and the stimulus function are synchronized, suggesting that precise timing of Ca2+ spikes controls navigation. We identified the peptide asterosap as a chemotactic factor of the starfish Asterias amurensis. The Ca2+ spikes and swimming behavior of sperm from starfish and sea urchin are similar, implying that the signaling pathway of chemotaxis has been conserved for almost 500 million years. [ABSTRACT FROM AUTHOR]

WW domains mediate protein-protein interactions in a number of different cellular functions by recognizing proline-containing peptide sequences. We determined peptide recognition propensities for 42 WW domains using NMR spectroscopy and peptide library screens. As potential ligands, we studied both model peptides and peptides based on naturally occurring sequences, including phosphorylated residues. Thirty-two WW domains were classified into six groups according to detected ligand recognition preferences for binding the motifs PPx(Y/ poY), (p/ϕ)P(p,g)PPpR, (p/ϕ)PPRgpPp, PPLPp, (p/ξ)PPPPP, and ( poS/ poT)P (motifs according to modified Seefeld Convention 2001). In addition to these distinct binding motifs, group-specific WW domain consensus sequences were identified. For PPxY-recognizing domains, phospho-tyrosine binding was also observed. Based on the sequences of the PPx(Y/ poY)-specific group, a profile hidden Markov model was calculated and used to predict PPx(Y/ poY)-recognition activity for WW domains, which were not assayed. PPx(Y/ poY)-binding was found to be a common property of NEDD4-like ubiquitin ligases. [ABSTRACT FROM AUTHOR]

Examines the role of nitric oxide synthase I peptides in the target recognition of apocalmodulin. Increase in the level of hydrophobic amino acids; Details on the binding of wild-type and mutant peptides to calcium-calmodulin; Absorption of peptide bonds.

This study documents the identity of a calcium‐ regulated membrane guanylate cyclase transduction system in the photoreceptor‐bipolar synaptic region. The guanylate cyclase is the previously characterized ROS‐GC1 from the rod outer segments and its modulator is S100β. S100β senses increments in free Ca2+ and stimulates the cyclase. Specificity of photoreceptor guanylate cyclase activation by S100β is validated by the identification of two S100β‐regulatory sites. A combination of peptide competition, surface plasmon resonance binding and deletion mutation studies has been used to show that these sites are specific for S100β and not for another regulator of ROS‐GC1, guanylate cyclase‐activating protein 1. One site comprises amino acids (aa) Gly962–Asn981, the other, aa Ile1030–Gln1041. The former represents the binding site. The latter binds S100β only marginally, yet it is critical for control of maximal cyclase activity. The findings provide evidence for a new cyclic GMP transduction system in synaptic layers and thereby extend existing concepts of how a membrane‐bound guanylate cyclase is regulated by small Ca2+‐sensor proteins. [ABSTRACT FROM AUTHOR]

The binding of peptides or proteins to a bilayer membrane is often coupled with a random coil→α-helix transition. Knowledge of the energetics of this membrane-induced folding event is essential for the understanding of the mechanism of membrane activity. In a recent study [Wieprecht et al., J. Mol. Biol. 294 (1999) 785–794], we have developed an approach which allows an analysis of the energetics of membrane-induced folding. We have systematically varied the helix content of the amphipathic peptide magainin-2-amide by synthesizing analogs where two adjacent amino acid residues were substituted by their corresponding d-enantiomers and have measured their binding to small unilamellar vesicles (SUVs). Correlation of the binding parameters with the helicities allowed the evaluation of the thermodynamic parameters of helix formation. Since SUVs (30 nm in diameter) are characterized by a non-ideal lipid packing due to their high membrane curvature, we have now extended our studies to large unilamellar vesicles (LUVs) (100 nm in diameter) with a lipid packing close to planar membranes. While the free energy of binding was similar for SUVs and LUVs, the binding enthalpies and entropies were distinctly different for the two membrane systems. The thermodynamic parameters of the coil–helix transition were nevertheless not affected by the vesicle size. Helix formation at the membrane surface of LUVs (SUVs) was characterized by an enthalpy change of −0.8 (−0.7) kcal/mol per residue, an entropy change of−2.3 (−1.9) cal/mol K per residue, and a free energy change of −0.12 (−0.14) kcal/mol per residue. Helix formation accounted for ∼50% of the free energy of binding underlining its major role as a driving force for membrane-binding. [Copyright &y& Elsevier]