The display of functional proteins on self-assembled peptide nanofibrils is challenging since the steric bulk of proteins attached to simple self-assembling peptides often impedes incorporation into nanofibrils. Herein is described a split-protein strategy to tether functional proteins to preassembled peptide nanofibrils. In this strategy, a short affinity motif peptide derived from a split protein system is appended to a self-assembly motif (the amphipathic Ac-(FKFE)2-NH2 peptide) to form an affinity-assembly fusion peptide. The small size of the affinity motif allows the affinity-assembly fusion peptide to be readily incorporated into peptide nanofibrils that display the affinity motif when the affinity-assembly peptide is coassembled with Ac-(FKFE)2-NH2. Introduction of the split-protein that is complementary to the affinity motif to the assembled nanofibrils results in efficient, multivalent attachment of functional proteins to the peptide nanofibrils. This strategy is demonstrated with two split-protein systems, ribonuclease S' (RNase S') and split green fluorescent protein (GFP).

Self-assembled peptide-based hydrogels are emerging materials that have been exploited for wound healing, drug delivery, tissue engineering, and other applications. In comparison to synthetic polymer hydrogels, supramolecular peptide-based gels have advantages in biocompatibility, biodegradability, and ease of synthesis and modification. Modification of the emergent viscoelasticity of peptide hydrogels in a stimulus responsive fashion is a longstanding goal in the development of next-generation materials. In an effort to selectively modulate hydrogel viscoelasticity, we report herein a method to enhance the elasticity of β-sheet peptide hydrogels using specific molecular recognition events between functionalized hydrogel fibrils and biomolecules. Two distinct biomolecular recognition strategies are demonstrated: oligonucleotide Watson-Crick duplex formation between peptide nucleic acid (PNA) modified fibrils with a bridging oligonucleotide and protein-ligand recognition between mannose modified fibrils with concanavalin A. These methods to modulate hydrogel elasticity should be broadly adaptable in the context of these materials to a wide variety of molecular recognition partners.

Excitotoxicity was originally postulated to be a late stage side effect of Alzheimer׳s disease (AD)-related neurodegeneration, however more recent studies indicate that it may occur early in AD and contribute to the neurodegenerative process. Tau and amyloid beta (Aβ), the main components of neurofibrillary tangles (NFTs) and amyloid plaques, have been implicated in cooperatively and independently facilitating excitotoxicity. Our study investigated the roles of tau and Aβ in AD-related excitotoxicity. In vivo studies showed that tau knockout (tau−/−) mice were significantly protected from seizures and hippocampal superoxide production induced with the glutamate analog, kainic acid (KA). We hypothesized that tau accomplished this by facilitating KA-induced Ca2+ influx into neurons, however lentiviral tau knockdown failed to ameliorate KA-induced Ca2+ influx into primary rat cortical neurons. We further investigated if tau cooperated with Aβ to facilitate KA-induced Ca2+ influx. While Aβ biphasically modulated the KA-induced Cacyt2+ responses, tau knockdown continued to have no effect. Therefore, tau facilitates KA-induced seizures and superoxide production in a manner that does not involve facilitation of Ca2+ influx through KA receptors (KAR). On the other hand, acute pretreatment with Aβ (10min) enhanced KA-induced Ca2+ influx, while chronic Aβ (24h) significantly reduced it, regardless of tau knockdown. Given previously published connections between Aβ, group 1 metabotropic glutamate receptors (mGluRs), and KAR regulation, we hypothesized that Aβ modulates KAR via a G-protein coupled receptor pathway mediated by group 1mGluRs. We found that Aβ did not activate group 1mGluRs and inhibition of these receptors did not reverse Aβ modulation of KA-induced Ca2+ influx. Therefore, Aβ biphasically regulates KAR via a mechanism that does not involve group 1mGluR activation.

Amyloid fibrils formed by peptides found in semen have been shown to enhance HIV infectivity in vitro. The first of these peptides to be identified was the 248–286 fragment of prostatic acid phosphatase (PAP248–286) (Munich et al., 2007). PAP248–286 is highly cationic, and its fibrils might facilitate infection by decreasing the electrostatic repulsion between the negatively charged surfaces of the virus and the target cell. Whereas PAP248–286 can easily form fibrils in seminal fluid, it needs rapid agitation in other environments, and certain ions have been shown to be critical for its assembly into fibrils (Olsen et al., 2012). However, mutation of the positively charged residues to alanine results in a peptide (PAP248–286Ala) that can more easily form fibrilar aggregates. We studied PAP248–286 and PAP248–286Ala fibril formation in water and water + NaCl environments. While PAP248-286Ala can efficiently form fibrils in both water and water + NaCl, PAP248-286 can only do so in a water + NaCl solution. The inability of PAP248–286 to form fibrils in water could be due solely to repulsion between the positively charged peptides, an effect that might be diminished by the presence of salt. However, it is also possible that the explanation lies in PAP248–286’s failure to populate conformations that can easily lead to ordered aggregates. To answer this question, using molecular dynamics simulations, we characterized the ensemble of conformations populated by the two peptides in water and water + NaCl environments. The results indicate that PAP248-286Ala favors contacts that stabilize a strand-turn-strand, or β-arch, motif around P31, the only proline residue in the sequence. Because β-arches are a common feature in amyloid fibrils, and because it is very unlikely that a proline residue would be in any position other than the β-arch, we expect the formation of this motif to be the rate-limiting step in PAP248–286Ala / PAP248–286 fibril formation. Moreover, the contacts stabilizing the β-arch would bring positively charged residues into contact in PAP248–286, which, consistent with the experimental results, would be facilitated by the presence of negative ions. To summarize, we have tried to understand if the inability of PAP248–286 to efficiently form fibrils in water is only due to a slower aggregation caused by electrostatic repulsion between the positively charged peptides. Our data suggest that this effect is also due to electrostatic repulsion between the residues within each monomeric peptide, which prevents PAP248–286 from populating conformations that would lead to ordered aggregates.

Cationic amyloid fibrils, including the Semen Enhancer of Virus Infection (SEVI), have recently been described in human semen. Simple methods for quantitating these fibrils are needed to improve our understanding of their biological function. We performed high-throughput screening to identify molecules that bind SEVI, and identified a small molecule (8E2), that fluoresced brightly in the presence of SEVI and other cationic fibrils. 8E2 bound SEVI with almost 40-fold greater affinity than thioflavin-T, and could efficiently detect high molecular weight fibrils in human seminal fluid.

We extend to you a warm and sunny Aloha in celebration of the 23 rd American Peptide Symposium and the 6 th International Symposium.The meeting theme, Peptides Across the Pacific, embraced the spirit of the scientific and social program.Peptides Across the Pacific encompassed the important role that peptide science currently plays in so many disciplines and explored the potential impact peptides can make in scientific fields that have yet to realize the utility of these wonderful molecules.The scientific program for 2013

Amyloid fibrils contained in semen, known as SEVI, or semen-derived enhancer of viral infection, have been shown to increase the infectivity of HIV dramatically. However, previous work with these fibrils has suggested that extensive time and nonphysiologic levels of agitation are necessary to induce amyloid formation from the precursor peptide (a proteolytic cleavage product of prostatic acid phosphatase, PAP(248-286)). Here, we show that fibril formation by PAP(248-286) is accelerated dramatically in the presence of seminal plasma (SP) and that agitation is not required for fibrillization in this setting. Analysis of the effects of specific SP components on fibril formation by PAP(248-286) revealed that this effect is primarily due to the anionic buffer components of SP (notably inorganic phosphate and sodium bicarbonate). Divalent cations present in SP had little effect on the kinetics of fibril formation, but physiologic levels of Zn(2+) strongly protected SEVI fibrils from degradation by seminal proteases. Taken together, these data suggest that in the in vivo environment, PAP(248-286) is likely to form fibrils efficiently, thus providing an explanation for the presence of SEVI in human semen.

Amphipathic peptides composed of alternating hydrophobic and hydrophilic amino acids self-assemble into amyloid-inspired, β-sheet nanoribbon fibrils. Herein, we report a new fibril type that is formed from equimolar mixtures of enantiomeric amphipathic peptides (L- and D-(FKFE)(2)). Spectroscopic analysis indicates that these peptides do not self-sort and assemble into enantiomeric fibrils composed of all-l and all-d peptides, but rather coassemble into fibrils that contain alternating L- and D-peptides in a "rippled β-sheet" orientation. Isothermal titration calorimetry indicates an enthalpic advantage for rippled β-sheet coassembly compared to self-sorted β-sheet assembly of enantiomeric peptides.

Semen-derived enhancer of viral infection (SEVI), an amyloid fibril formed from a cationic peptide fragment of prostatic acidic phosphatase (PAP), dramatically enhances the infectivity of human immunodeficiency virus type 1 (HIV-1). Insoluble, sedimentable fibrils contribute to SEVI-mediated enhancement of virus infection. However, the SEVI-forming PAP(248-286) peptide is able to produce infection-enhancing structures much more quickly than it forms amyloid fibrils. This suggests that soluble supramolecular assemblies may enhance HIV-1 infection. To address this question, non-SEVI amyloid-like fibrils were derived from general amphipathic peptides of sequence Ac-K-n(XKXE)(2)-NH2. These cationic peptides efficiently self-assembled to form soluble, fibril-like structures that were, in some cases, able to enhance HIV-1 infection even more efficiently than SEVI. Experiments were also performed to determine whether agents that efficiently shield the charged surface of SEVI fibrils block SEVI-mediated infection-enhancement. To do this, we generated self-assembling anionic peptides of sequence Ac-E-n(XKXE)(2)-NH2. One of these peptides completely abrogated SEVI-mediated enhancement of HIV-1 infection, without altering HIV-1 infectivity in the absence of SEVI. Collectively, these data suggest that soluble SEVI assemblies may mediate infection-enhancement, and that anionic peptide supramolecular assemblies have the potential to act as anti-SEVI microbicides.