Unzipping the role of chirality in nanoscale self-assembly of tripeptide hydrogels

Abstract

Change of chirality is a useful tool to manipulate the aqueous self-assembly behaviour of uncapped, hydrophobic tripeptides. In contrast with other short peptides, these tripeptides form hydrogels at a physiological pH without the aid of organic solvents or end-capping groups (e.g. Fmoc). The novel hydrogel forming peptide (D)Leu-Phe-Phe ((D)LFF) and its epimer Leu-Phe-Phe (LFF) exemplify dramatic supramolecular effects induced by subtle changes to stereochemistry. Only the d-amino acid-containing peptide instantly forms a hydrogel in aqueous solution following a pH switch, generating long fibres (>100 μm) that entangle into a 3D network. However, unexpected nanostructures are observed for both peptides and they are particularly heterogeneous for LFF. Structural analyses using CD, FT-IR and fluorescent amyloid staining reveal anti-parallel beta-sheets for both peptides. XRD analysis also identifies key distances consistent with beta-sheet formation in both peptides, but suggests additional high molecular order and extended molecular length for (D)LFF only. Molecular modelling of the two peptides highlights the key interactions responsible for self-assembly; in particular, rapid self-assembly of (D)LFF is promoted by a phenylalanine zipper, which is not possible because of steric factors for LFF. In conclusion, this study elucidates for the first time the molecular basis for how chirality can dramatically influence supramolecular organisation in very short peptide sequences.

Biological Water Dynamics and Entropy: A Biophysical Origin of Cancer and Other Diseases

“…In 2001, Aggeli et al presented a generic statistical mechanical model for the self-assembly of chiral rod-like units, such as beta-sheet-forming peptides, into helical tapes, which, with increasing concentration, associate into twisted ribbons (double tapes), fibrils (twisted stacks of ribbons), and fibers (entwined fibrils) [179]. Results of a recent study of self-assembly behavior of isomers of the hydrophobic tripeptide leu-phe-phe suggest that proteins composed of homochiral amino acids would likely assemble and pack more efficiently than those containing both D-and L-amino acids [180].…”

Exploring the sequence space for (tri-)peptide self-assembly to design and discover new hydrogels

“…Experimentally, a small set of tripeptides has been reported to assemble into nanostructures in (mainly) aqueous environments: for example, CFF forms nanospheres; FFF forms fibrous and plate-like assemblies 6,7 ; VFF, FFV and LFF form heterogeneous nanostructures [9][10][11] ; micelle formation was discovered in VYV 12 and KFG 8 (which in the latter case could be converted reversibly to nanotubes by lowering the pH); disordered aggregates were found upon drying a solution of DFN 13 . One common approach to alter the self-assembly properties of short peptides is protection of the terminal amine or acid groups with acetyl [14][15][16][17][18] , t-butyloxycarbonyl 19,20 or large aromatic groups [21][22][23][24] , thereby reducing charge repulsions and introducing π-stacking/hydrophobic contributions to favour self-assembly and gelation.…”

The unexpected advantages of using D-amino acids for peptide self-assembly into nanostructured hydrogels for medicine

“…In particular, we observed that, under conditions at which the homochiral sequences Val-Phe-Phe, Phe-Phe-Val, or Leu-Phe-Phe do not gel, their heterochiral analogues bearing a D-amino acid at the N-terminal rapidly form selfsupportive hydrogels based on antiparallel beta-sheets [34,37]. Interestingly, despite the very subtle differences in amino acid sequence, the three heterochiral peptides Leu-Phe-Phe form different nanostructures, i.e., nanotapes, twisted fibers, and thick bundles, respectively [34,37]. Molecular modelling and XRD studies point to a supramolecular stabilizing effect played by heterochirality.…”

“…By contrast with the homochiral stereoisomers, presence of both D-and L-amino acids removes key steric clashes between side chains, and allows for the formation of peptide stacks that interdigitate via phenylalanine zippers into superstructures with hierarchical order [37]. As a result, gelation occurs as rapidly as within seconds, as shown in a video [37]. Fig.…”