Peptide assembly structures have been widely exploited in fabricating biomaterials that are promising for medical applications. Peptides can self-organize into various highly ordered supramolecular architectures, such as nanofibril, nanobelt, nanotube, nanowire, and vesicle. Detailed studies of the molecular mechanism by which these versatile building blocks assemble can guide the design of peptide architectures with desired structure and functionality. It has been revealed that peptide assembly structures are highly sequence-dependent and sensitive to amino acid composition, the chirality of peptide and amino acid residues, and external factors, such as solvent, pH, and temperature. This mini-review focuses on the regulatory effects of chirality alteration on the structure and bioactivity of linear and cyclic peptide assemblies. In addition, chiral self-sorting and co-assembly of racemic peptide mixtures were discussed.

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Amino acid chirality has been envisioned as an important strategy to regulate structure and function of peptide self-assembled architectures. However, the molecular mechanism of chirality effects in peptide assemblies remains largely elusive. Here, the assembly structures of l-peptide polyphenylalanine F10 (FFFF­FFF­FFF) and block heterochiral peptide F5f5 (FFFFF­fffff) composed of two FFFFF repeat blocks with opposite chirality were characterized at the single-molecule level by using scanning tunneling microscopy. Each peptide formed two distinctively different assembly structures on the HOPG surface, in which peptide chains took parallel and antiparallel β-sheet conformations, respectively. The molecular-level observations revealed that the staggered arrangement of cross-strand side chains achieved in the antiparallel β-sheet structure of the block heterochiral peptide facilitated intimate packing of side chains and maximized inter-residue van der Waals interactions, which led to more residues participating in assembly and greatly stabilized the β-sheet structure of the surface-bound peptide assembly, but such cross-strand nested interactions were not accessible in the heterochiral parallel β-sheet structure and the enantiomerically pure assembly structures. This work could contribute to the molecular insights of stereochemical interactions in peptide assemblies and feasibility of extending this block heterochirality pattern to other peptides with various lengths and amino acid compositions for structural regulations.

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