Modulating Supramolecular Peptide Hydrogel Viscoelasticity Using Biomolecular Recognition.

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 ß-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.

Display of functional proteins on supramolecular peptide nanofibrils using a split-protein strategy.

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).

Fluorescence detection of cationic amyloid fibrils in human semen.

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.

Coassembly of enantiomeric amphipathic peptides into amyloid-inspired rippled ß-sheet fibrils.

Amphipathic peptides composed of alternating hydrophobic and hydrophilic amino acids self-assemble into amyloid-inspired, ß-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 ß-sheet" orientation. Isothermal titration calorimetry indicates an enthalpic advantage for rippled ß-sheet coassembly compared to self-sorted ß-sheet assembly of enantiomeric peptides.

Seminal plasma accelerates semen-derived enhancer of viral infection (SEVI) fibril formation by the prostatic acid phosphatase (PAP248-286) peptide.

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.

Enhancement of HIV-1 infectivity by simple, self-assembling modular 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)-NH(2). 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)-NH(2). 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.