Search

Engineered destruction of target proteins by recruitment to the cell’s degradation machinery has emerged as a promising strategy in drug discovery. The majority of molecules that facilitate targeted degradation do so via a select number of ubiquitin ligases, restricting this therapeutic approach to tissue types that express the requisite ligase. Here, we describe a new strategy of targeted protein degradation through direct substrate recruitment to the 26S proteasome. The proteolytic complex is essential and abundantly expressed in all cells; however, proteasomal ligands remain scarce. We identify potent peptidic macrocycles that bind directly to the 26S proteasome subunit PSMD2, with a 2.5-Å-resolution cryo-electron microscopy complex structure revealing a binding site near the 26S pore. Conjugation of this macrocycle to a potent BRD4 ligand enabled generation of chimeric molecules that effectively degrade BRD4 in cells, thus demonstrating that degradation via direct proteasomal recruitment is a viable strategy for targeted protein degradation.

Autophagy-related proteins (Atgs) drive the lysosome-mediated degradation pathway, autophagy, to enable the clearance of dysfunctional cellular components and maintain homeostasis. In humans, this process is driven by the mammalian Atg8 (mAtg8) family of proteins comprising the LC3 and GABARAP subfamilies. The mAtg8 proteins play essential roles in the formation and maturation of autophagosomes and the capture of specific cargo through binding to the conserved LC3-interacting region (LIR) sequence within target proteins. Modulation of interactions of mAtg8 with its target proteins via small-molecule ligands would enable further interrogation of their function. Here we describe unbiased fragment and DNA-encoded library (DEL) screening approaches for discovering LC3 small-molecule ligands. Both strategies resulted in compounds that bind to LC3, with the fragment hits favoring a conserved hydrophobic pocket in mATG8 proteins, as detailed by LC3A-fragment complex crystal structures. Our findings demonstrate that the malleable LIR-binding surface can be readily targeted by fragments; however, rational design of additional interactions to drive increased affinity proved challenging. DEL libraries, which combine small, fragment-like building blocks into larger scaffolds, yielded higher-affinity binders and revealed an unexpected potential for reversible, covalent ligands. Moreover, DEL hits identified possible vectors for synthesizing fluorescent probes or bivalent molecules for engineering autophagic degradation of specific targets.

Coal spoil-heaps cause man-made pressure on the environment of the coal mining area. Coal mining, and in recent years the mass closure of mines has been accompanied by a negative impact on natural objects and engineering structures - the basements of houses and buildings are flooded, walls and wooden fences rot, crops, trees and bushes are destroyed. Reclamation is carried out on spoil-heaps of coal mines to reduce man-made pressure. However, in the process of rock dumping on the spoil-heaps a neorelief begins to emerge causing the vegetation development. The emergence of vegetation groups is a positive phenomenon, as phytomass decomposition promotes the formation of humus. The development of vegetation on the surface of coal spoil-heaps is called vegetative reclamation or phytomelioration. Efficiency of vegetative reclamation is calculated in points and is an indicator of the suitability of a particular man-made object for natural overgrowth. The aim of the work is to establish the features of spatial arrangement of plants in populations on the surface of coal spoil-heaps. It is established that on the coal spoil-heaps, as well as in natural conditions, vegetation tends to aggregate, thus forming phytogenic fields. It should be noted that at different stages of successions, phytogenic fields are formed in different ways. Monocentric phytogenic field arises on the waste heaps during the syngenetic stage of succession. The initial endecogenetic stage of succession provides the formation of phytogenic fields of two types. The first type is the initial polycentric phytogenic field. It is characterized by the ability to combine several individuals of the same species. The second type is a mature polycentric phytogenic field. It is characterized by higher resistance, and plant community is already able to convert geoprocesses. The mature endoecogenic stage of succession is characterized by the development and expansion of tree species, and the phytogenic field is acentric and global. This kind of phytogenic fields is found on tailings with artificial vegetative reclamation.

Polyubiquitination is a complex form of posttranslational modification responsible for the control of numerous cellular processes. Many ubiquitin-binding proteins recognize distinct polyubiquitin chain types, and these associations help drive ubiquitin-signaling pathways. There is considerable interest in understanding the specificity of ubiquitin-binding proteins; however, because of the multivalent nature of polyubiquitin, affinity measurements of these interactions that rely on affixing ubiquitin-binding proteins to a surface can display artifactual, method-dependent avidity, or "bridging." This artifact, which is distinct from biologically relevant, avid interactions with polyubiquitin, is commonplace in such polyubiquitin-binding measurements and can lead to dramatic overestimations of binding affinities for particular chain types, and thus, incorrect conclusions about specificity. Here, we use surface-based measurements of ubiquitin binding in three model systems to illustrate bridging and lay out practical ways of identifying and mitigating it. Specifically, we describe a simple fitting model that enables researchers to diagnose the severity of bridging artifacts, determine whether they can be minimized, and more accurately evaluate polyubiquitin-binding specificity.

The content of heavy metals, radionuclides, nitrates in edible mushrooms is a topical issue for many researchers in the world. However, such issues on edible mushrooms, in particular, Pleurotus ostreatus, which are found naturally within a large city, require more detailed studies because these mushrooms are used in human nutrition. It was found that in some areas, the cadmium content in the studied oyster mushroom specimens is three times higher than the maximum permissible concentration (0.092-0.095 mg / kg). The lead content in the fruiting bodies of oyster mushroom is in the range of maximum permissible concentration (MPC) and is 0.19-0.22 mg / kg. The content of mobile forms of copper exceeded the MPC only in two cases - 5.72 mg / kg and 5.06 mg / kg. The zinc content was 8.87-13.41 mg / kg with MPC being 10 mg / kg. The content of 137Cs was in the range of 0.095-0.1 Bq / kg and that of 90Sr was 0.3-0.4 Bq / kg, which does not exceed the MPC. The content of nitrates in the fruiting bodies of oyster mushrooms did not exceed the maximum permissible concentration of 50 mg / kg. Considering the data obtained on the content of heavy metals, radionuclides and nitrates in Pleurotus ostreatus, it should be noted that it is risky to eat such fruiting bodies that have developed in the urban-ecological environment.

Oyster mushroom (Pleurotus ostreatus(Jacq. ex Fr.)P. Kumm.) is involved in the destruction of dead wood which is the main place of settlement of several living organisms.After humification, dead wood also becomes an important component of forest soils.The purpose of the research is to study temperature and moisture conditions of extensive cultivation of oyster mushrooms on various wood substrates.To accomplish this goal, the following tasks were set: to determine the amount of effective stress temperatures and moisture content of substrates and their influence on the appearance of fruiting bodies of the oyster mushroom;to study the featuresof the extensive cultivation of oyster mushrooms on the tree stumps of cutover areas, in the hollows of broadleaved trees, using brushwood, on inoculated log sections in trenches, on log sections ofdead dry trees. The oyster mushroom fruiting bodies collected in the suburban forest formed the basis of the experiment on the inoculation of different types of substrates.The inoculation of the log sections was carried with a relative air humidity of 85%, the process of overgrowing lasted from 2 to 3 months.The edaphic-climatic factors of different types of space -closed and open -were taken into account.The amountof effective temperatures necessary for the development of fruiting bodies has been determined. It was foundthat the intensive growth of the mushroom fruiting bodies begins after a sharp cooling (a drop in night temperatures to 4-8 ° C), which causes a stressful state of the mushroom. The amountof the effective stress temperatures is4.6 ° C. Long-term phenological observations have revealedthat the amountof the effective temperatures in the spring is 76.4 ° C, and in the autumn-59.4 ° C. The duration of fruiting of oyster mushroom on log sectionsof hardwoodsis 14 days in springand 17 days in autumn longer than on softwoods blocks. It was foundthat the biomass of the fruiting bodies is directly dependent on the thickness of the log section, and,therefore,it is recommended to use log sectionsranging from 35 cm to 50 cm in diameter and up to 30 cm in length.

Thesis deals with automated corpus development techniques for specific linguistic research purposes. Different corpora and corpus toolboxes available today have been overviewed. Corpus tool functionality for processing custom and private text purposes and automated corpora building system capabilities has been classified. Lack of analytical means which decrease effectiveness, multifunctionality and adaptability in overviewed corpora has been illustrated (impossibility of FrameNet usage, lack of detailed statistics and other relevant issues). Main stages of source data text processing have been reviewed. Natural language processing and natural language understanding methods and tools for adaptable corpora building have been examined and justified. General workflow and design of adaptable text corpus software tool are suggested. Adaptable text corpus software prototype for specific linguistic research purposes has been developed. Big Data and text search engine approaches have been implemented in the prototype.

The atomic composition, local structure and coordination of flash evaporated Ge2S3 films and their changes induced by laser illumination and thermal annealing in vacuum were investigated by means of high resolution synchrotron radiation and X-ray photoelectron spectroscopy. The top surface and subsurface layers of the films are found to be enriched by Ge in comparison with the composition of target glass and contain oxygen and a significant contribution of physisorbed carbon. The influence of laser and thermal treatments of flash evaporated Ge–S films in vacuum on their composition is analyzed. The local atomic coordination obtained by curve fitting of Ge 3d, S 2p, O 1s and C 1s core level spectra is discussed in detail.

Плівки Ge 2 S 3 були виготовлені методом дискретного термічного випаровування порошку і досліджувалися методом фотоелектронної спектроскопії. Досліджені СФС і РФС спектри опромінених лазером та відпалених плівок Ge 2 S 3 . Також проаналізовані зміни параметрів фото­електрон­них спектрів плівок, індуковані лазерним опроміненням з енергією, близькою до ширини забороненої зони, і термічним відпалом. Обговорюється вплив окислення Ge у при поверхневих шарах на структурні зміни у плівці.

Microsomal cytochrome b5 (cytb5) is a membrane-bound protein that modulates the catalytic activity of its redox partner, cytochrome P4502B4 (cytP450). Here, we report the first structure of full-length rabbit ferric microsomal cytb5 (16 kDa), incorporated in two different membrane mimetics (detergent micelles and lipid bicelles). Differential line broadening of the cytb5 NMR resonances and site-directed mutagenesis data were used to characterize the cytb5 interaction epitope recognized by ferric microsomal cytP450 (56 kDa). Subsequently, a data-driven docking algorithm, HADDOCK (high ambiguity driven biomolecular docking), was used to generate the structure of the complex between cytP4502B4 and cytb5 using experimentally derived restraints from NMR, mutagenesis, and the double mutant cycle data obtained on the full-length proteins. Our docking and experimental results point to the formation of a dynamic electron transfer complex between the acidic convex surface of cytb5 and the concave basic proximal surface of cytP4502B4. The majority of the binding energy for the complex is provided by interactions between residues on the C-helix and β-bulge of cytP450 and residues at the end of helix α4 of cytb5. The structure of the complex allows us to propose an interprotein electron transfer pathway involving the highly conserved Arg-125 on cytP450 serving as a salt bridge between the heme propionates of cytP450 and cytb5. We have also shown that the addition of a substrate to cytP450 likely strengthens the cytb5-cytP450 interaction. This study paves the way to obtaining valuable structural, functional, and dynamic information on membrane-bound complexes.

Recently, a 39 amino acid peptide fragment from prostatic acid phosphatase has been isolated from seminal fluid that can enhance infectivity of the HIV virus by up to four to five orders of magnitude. PAP(248–286) is effective in enhancing HIV infectivity only when it is aggregated into amyloid fibers termed SEVI. The polyphenol EGCG (epigallocatechin-3-gallate) has been shown to disrupt both SEVI formation and HIV promotion by SEVI, but the mechanism by which it accomplishes this task is unknown. Here we show that EGCG interacts specifically with the side-chains of monomeric PAP(248–286) in two regions (K251-R257 and N269-I277) of primarily charged residues, particularly lysine. The specificity of interaction to these two sites is contrary to previous studies on the interaction of EGCG with other amyloidogenic proteins, which showed the nonspecific interaction of EGCG with exposed backbone sites of unfolded amyloidogenic proteins. This interaction is specific to EGCG as the related gallocatechin (GC) molecule, which shows greatly decreased anti-amyloid activity, exhibits minimal interaction with monomeric PAP(248–286). The EGCG binding was shown to occur in two steps, with the initial formation of a weakly bound complex followed by a pH dependent formation of a tightly bound complex. Experiments in which the lysine residues of PAP(248–286) have been chemically modified suggest the tightly bound complex is created by Schiff-base formation with lysine residues. The results of this study could aid in the development of small molecule inhibitors of SEVI and other amyloid proteins.

Inactivation of the TNFAIP3 gene, encoding the A20 protein, is associated with critical inflammatory diseases including multiple sclerosis, rheumatoid arthritis and Crohn's disease. However, the role of A20 in attenuating inflammatory signalling is unclear owing to paradoxical in vitro and in vivo findings. Here we utilize genetically engineered mice bearing mutations in the A20 ovarian tumour (OTU)-type deubiquitinase domain or in the zinc finger-4 (ZnF4) ubiquitin-binding motif to investigate these discrepancies. We find that phosphorylation of A20 promotes cleavage of Lys63-linked polyubiquitin chains by the OTU domain and enhances ZnF4-mediated substrate ubiquitination. Additionally, levels of linear ubiquitination dictate whether A20-deficient cells die in response to tumour necrosis factor. Mechanistically, linear ubiquitin chains preserve the architecture of the TNFR1 signalling complex by blocking A20-mediated disassembly of Lys63-linked polyubiquitin scaffolds. Collectively, our studies reveal molecular mechanisms whereby A20 deubiquitinase activity and ubiquitin binding, linear ubiquitination, and cellular kinases cooperate to regulate inflammation and cell death.

The cAMP-mediated allosteric transition in the catabolite activator protein (CAP; also known as the cAMP receptor protein, CRP) is a textbook example of modulation of DNA-binding activity by small-molecule binding. Here we report the structure of CAP in the absence of cAMP, which, together with structures of CAP in the presence of cAMP, defines atomic details of the cAMP-mediated allosteric transition. The structural changes, and their relationship to cAMP binding and DNA binding, are remarkably clear and simple. Binding of cAMP results in a coil-to-helix transition that extends the coiled-coil dimerization interface of CAP by 3 turns of helix and concomitantly causes rotation, by approximately 60 degrees , and translation, by approximately 7 A, of the DNA-binding domains (DBDs) of CAP, positioning the recognition helices in the DBDs in the correct orientation to interact with DNA. The allosteric transition is stabilized further by expulsion of an aromatic residue from the cAMP-binding pocket upon cAMP binding. The results define the structural mechanisms that underlie allosteric control of this prototypic transcriptional regulatory factor and provide an illustrative example of how effector-mediated structural changes can control the activity of regulatory proteins.

NADPH-cytochrome P450 oxidoreductase (CYPOR) is an essential redox partner of the cytochrome P450 (cyt P450) superfamily of metabolic enzymes. In the endoplasmic reticulum of liver cells, such enzymes metabolize ∼75% of the pharmaceuticals in use today. It is known that the transmembrane domain of CYPOR plays a crucial role in aiding the formation of a complex between CYPOR and cyt P450. Here we present the transmembrane structure, topology, and dynamics of the FMN binding domain of CYPOR in a native membrane-like environment. Our solid-state NMR results reveal that the N-terminal transmembrane domain of CYPOR adopts an α-helical conformation in the lipid membrane environment. Most notably, we also show that the transmembrane helix is tilted ∼13° from the lipid bilayer normal, and exhibits motions on a submillisecond timescale including rotational diffusion of the whole helix and fluctuation of the helical director axis. The approaches and the information reported in this study would enable further investigations on the structure and dynamics of the full-length NADPH-cytochrome P450 oxidoreductase and its interaction with other membrane proteins in a membrane environment.

Fragments of prostatic acid phosphatase (PAP248-286) in human semen dramatically increase HIV infection efficiency by increasing virus adhesion to target cells. PAP248-286 only enhances HIV infection in the form of amyloid aggregates termed SEVI (Semen Enhancer of Viral Infection), however monomeric PAP248-286 aggregates very slowly in isolation. It has therefore been suggested that SEVI fiber formation in vivo may be promoted by exogenous factors. We show here that a bacterially-produced extracellular amyloid (curli or Csg) acts as a catalytic agent for SEVI formation from PAP248-286 at low concentrations in vitro, producing fibers that retain the ability to enhance HIV (Human Immunodeficiency Virus) infection. Kinetic analysis of the cross-seeding effect shows an unusual pattern. Cross-seeding PAP248-286 with curli only moderately affects the nucleation rate while significantly enhancing the growth of fibers from existing nuclei. This pattern is in contrast to most previous observations of cross-seeding, which show cross-seeding partially bypasses the nucleation step but has little effect on fiber elongation. Seeding other amyloidogenic proteins (IAPP (islet amyloid polypeptide) and Aβ1-40) with curli showed varied results. Curli cross-seeding decreased the lag-time of IAPP amyloid formation but strongly inhibited IAPP elongation. Curli cross-seeding exerted a complicated concentration dependent effect on Aβ1-40 fibrillogenesis kinetics. Combined, these results suggest that the interaction of amyloidogenic proteins with preformed fibers of a different type can take a variety of forms and is not limited to epitaxial nucleation between proteins of similar sequence. The ability of curli fibers to interact with proteins of dissimilar sequences suggests cross-seeding may be a more general phenomenon than previously supposed.

Human Islet Amyloid Polypeptide (hIAPP) is a highly amyloidogenic protein found in islet cells of patients with type II diabetes. Because hIAPP is highly toxic to beta-cells under certain conditions, it has been proposed that hIAPP is linked to the loss of beta-cells and insulin secretion in type II diabetics. One of the interesting questions surrounding this peptide is how the toxic and aggregation prone hIAPP peptide can be maintained in a safe state at the high concentrations that are found in the secretory granule where it is stored. We show here zinc, which is found at millimolar concentrations in the secretory granule, significantly inhibits hIAPP amyloid fibrillogenesis at concentrations similar to those found in the extracellular environment. Zinc has a dual effect on hIAPP fibrillogenesis: it increases the lag-time for fiber formation and decreases the rate of addition of hIAPP to existing fibers at lower concentrations, while having the opposite effect at higher concentrations. Experiments at an acidic pH which partially neutralizes the change in charge upon zinc binding show inhibition is largely due to an electrostatic effect at His18. High-resolution structures of hIAPP determined from NMR experiments confirm zinc binding to His18 and indicate zinc induces localized disruption of the secondary structure of IAPP in the vicinity of His18 of a putative helical intermediate of IAPP. The inhibition of the formation of aggregated and toxic forms of hIAPP by zinc provides a possible mechanism between the recent discovery of linkage between deleterious mutations in the SLC30A8 zinc transporter, which transports zinc into the secretory granule, and type II diabetes.

Despite the rapid progress of the AIDS pandemic, the HIV virus is a surprisingly weak pathogen in vitro. The large difference between in vitro and in vivo infection rates suggests that cofactors absent in vitro but essential for the natural transmission of the virus may be responsible for this discrepancy. A recently identified peptide in human semen, PAP248-286, has emerged as a clear candidate for the missing cofactor as it dramatically enhances the infectivity of HIV by up to five orders of magnitude. PAP248-286 appears to enhance HIV infection by forming amyloid fibers known as SEVI, which are believed to enhance the attachment of the virus by bridging interactions between virion and host-cell membranes. To understand the unique ability of SEVI to enhance HIV infection, we have solved the atomic-level resolution structure of the SEVI precursor PAP248-286 using NMR spectroscopy in SDS micelles. In contrast to other toxic amyloid peptides that generally penetrate into the core of the membrane, non-toxic PAP248-286 binds superficially to the surface of the micelle. Unlike most amyloid peptides that bind to the membrane in an α-helical state, PAP248-286 is mostly disordered when bound to the surface of the micelle. The highly disordered nature of the SEVI peptide may explain the high ability of SEVI to enhance HIV infection, as partially disordered amyloid fibers will have a greater capture radius for the virus than more compact amyloid fibers. Two regions of nascent structure match the prediction of highly amyloidogenic sequences and may serve as nuclei for aggregation and amyloid fibril formation. NMR studies of the binding of PAP248-286 to the anti-amyloid agent ECGC will also be presented.

Semen is the main vector for HIV transmission worldwide. Recently, a peptide fragment (PAP(248-286)) has been isolated from seminal fluid that dramatically enhances HIV infectivity by up to 4-5 orders of magnitude. PAP(248-286) appears to enhance HIV infection by forming amyloid fibers known as SEVI, which are believed to enhance the attachment of the virus by bridging interactions between virion and host-cell membranes. We have solved the atomic-level resolution structure of the SEVI precursor PAP(248-286) using NMR spectroscopy in SDS micelles, which serve as a model membrane system. PAP(248-286), which does not disrupt membranes like most amyloid proteins, binds superficially to the surface of the micelle, in contrast to other membrane-disruptive amyloid peptides that generally penetrate into the core of the membrane. The structure of PAP(248-286) is unlike most amyloid peptides in that PAP(248-286) is mostly disordered when bound to the surface of the micelle, as opposed to the alpha-helical structures typically found of most amyloid proteins. The highly disordered nature of the SEVI peptide may explain the unique ability of SEVI amyloid fibers to enhance HIV infection as partially disordered amyloid fibers will have a greater capture radius for the virus than compact amyloid fibers. Two regions of nascent structure (an alpha-helix from V262-H270 and a dynamic alpha/3(10) helix from S279-L283) match the prediction of highly amyloidogenic sequences and may serve as nuclei for aggregation and amyloid fibril formation. The structure presented here can be used for the rational design of mutagenesis studies on SEVI amyloid formation and viral infection enhancement.

Allosteric interactions are typically considered to proceed through a series of discrete changes in bonding interactions that alter the protein conformation. Here we show that allostery can be mediated exclusively by transmitted changes in protein motions. We have characterized the negatively cooperative binding of cAMP to the dimeric catabolite activator protein (CAP) at discrete conformational states. Binding of the first cAMP to one subunit of CAP dimer has no effect on the conformation of the other subunit. The dynamics of the system, however, are modulated in a distinct way by the sequential ligand binding process, with the first cAMP partially enhancing and the second cAMP completely quenching protein motions. As a result, a pronounced conformational entropic penalty is incurred by the second cAMP binding that is entirely responsible for the observed cooperativity. The results provide strong support of the existence of purely dynamics-driven allostery.

Despite the rapid progress of the AIDS pandemic, HIV is a surprisingly weak pathogen in vitro. The large difference between in vitro and in vivo infection rates suggests that cofactors absent in vitro but essential for the natural transmission of the virus may be responsible for this discrepancy. A recently identified peptide in human semen, PAP248-286, has emerged as a candidate for the missing cofactor as it dramatically enhances the infectivity of HIV by up to five orders of magnitude. The PAP248-286 peptide fragment has been shown to only induce its synergistic effect with HIV infection when in the form of amyloid fibers. Amyloid formation by PAP248-286 into the active SEVI form is a slow process during which it is susceptible to being degraded and inactivated. Therefore, initiators of this fibrillization process would be an indirect cause of the increase in viral infectivity. For this reason, we have searched for possible inhibitors and enhancers of SEVI amyloid formation including metals, lipids, other amyloids, and polyphenolic inhibitors. The effects of the metals are metal specific, with some enhancing kinetics, while others either inhibit or have little effect. High resolution structures of PAP248-286 and the green tea extract compound epigallocatechin gallate (EGCG) show binding to the monomer subunit through the lysine side-chains and inhibiting fiber growth, which could prove as an effective preventative measure for HIV infection. In contrast, amyloidogenic fibers produced by E. coli are seen to strongly enhance the kinetics of SEVI formation and HIV infectivity, indicating that bacterial infection could enhance the probability of HIV transmission. This phenomenon appears to be quite general and could be an important seeding mechanism for other amyloid proteins.1) Biophysical. Journal (2009), 97(9), 2474-2483.2) Biochemica et Biophysica Acta, Biomembranes (2011), 1808(4), 1161-1169.

Proteins misfolded into insoluble, fibrillar aggregates known as amyloid are a pathological feature of many common and devastating diseases. Amyloid formation is typically a slow process that can be strongly affected by extrinsic factors, among the most critical being the presence of a small amount of preformed seeds that serves to nucleate aggregation. Amyloid nucleation is often considered a highly specific process dependent on a high degree of similarity in both peptide sequence and fiber morphology. However, we show here that amyloid fibers known as curli that are produced in E. coli and related bacteria catalyze amyloid formation of a variety of dissimilar amyloidogenic peptides and proteins, including PAP248-286 (SEVI), insulin, and calcitonin. The preformed curli fibers appear to act as a nucleation site for amyloidogenic proteins and as such, can decrease the induction time, sometimes drastically, and induce the formation of fibers. In particular, cross-seeding of SEVI amyloid formation by curli was more effective than seeding the reaction with SEVI amyloid fibers obtained under a different reaction condition. The elongation rate of fiber formation is also increased for some (but not all) of the proteins tested, indicating curli can also increase in some circumstances the rate of addition of proteins to the ends of amyloid fibers. Curli and curli-like amyloid fibers are ubiquitous in mammalian hosts, in fact, the innate immune response common to almost all amyloids has been proposed to have evolved as a response to curli amyloid formation by E. Coli. Given that certain bacteria that express a curli-like protein colocalize with amyloid deposits in Alzheimer?s patients, the induction of amyloid formation by curli may be a factor of high clinical importance.

Amyloid fibers in human semen known as SEVI (semen-derived enhancer of viral infection) dramatically increase the infectivity of HIV and other enveloped viruses, which appears to be linked to the promotion of bridging interactions and the neutralization of electrostatic repulsion between the host and the viral cell membranes. The SEVI precursor PAP(248-286) is mostly disordered when bound to detergent micelles, in contrast to the highly α-helical structures found for most amyloid proteins. To determine the origin of this difference, the structures of PAP(248-286) were solved in aqueous solution and with 30% and 50% trifluoroethanol. In solution, pulsed field gradient (PFG)-NMR and (1)H-(1)H NOESY experiments indicate that PAP(248-286) is unfolded to an unusual degree for an amyloidogenic peptide but adopts significantly helical structures in TFE solutions. The clear differences between the structures of PAP(248-286) in TFE and SDS indicate electrostatic interactions play a large role in the folding of the peptide, consistent with the slight degree of penetration of PAP(248-286) into the hydrophobic core of the micelle. This is another noticeable difference between PAP(248-286) and other amyloid peptides, which generally show penetration into at least the headgroup region of the bilayer, and may explain some of the unusual properties of SEVI.