Abstract
Inspired by the key role of super-helical motifs in molecular self-organization, several tandem heptad repeat peptides were used as building blocks to form well-ordered supramolecular nano-assemblies. However, the need for stable helical structures limits the length of the smallest described units to three heptad repeats. Here we describe the first-ever self-assembling single heptad repeat module, based on the ability of the non-coded α-aminoisobutyric acid to stabilize very short peptides in helical conformation. A conformationally constrained peptide comprised of aromatic, but not aliphatic, residues, at the first and fourth positions formed helical fibrillar assemblies. Single crystal X-ray analysis of the peptide demonstrates super-helical packing in which phenylalanine residues formed an ‘aromatic zipper' arrangement at the molecular interface. The modification of the minimal building block with positively charged residues results in tight DNA binding ascribed to the combined factors of helicity, hydrophobicity and charge. The design of these peptides defines a new direction for assembly of super-helical nanostructures by minimal molecular elements.
Highlights
Inspired by the key role of super-helical motifs in molecular self-organization, several tandem heptad repeat peptides were used as building blocks to form well-ordered supramolecular nano-assemblies
The canonical helical segment is composed of a recurring sequence of seven amino acids known as a heptad repeat and designated as abcdefg, where positions a and d are often occupied by hydrophobic amino acids such as leucine, isoleucine and valine
We describe for the first time the design and formation of a super-helical structure formed by the molecular self-assembly of a single heptad peptide sequence
Summary
Inspired by the key role of super-helical motifs in molecular self-organization, several tandem heptad repeat peptides were used as building blocks to form well-ordered supramolecular nano-assemblies. The modification of the minimal building block with positively charged residues results in tight DNA binding ascribed to the combined factors of helicity, hydrophobicity and charge The design of these peptides defines a new direction for assembly of super-helical nanostructures by minimal molecular elements. Several others peptides that have the propensity for helical super structure formation were designed by modifying the nature of hydrophobic amino acids in the core as well as the characteristics of the residual heptad positions These designer building blocks self-assembled into distinct nanostructures having morphology ranging from fibres to net-like architectures to vesicles[22,23,24,25,26,27]. The minimal modification of the original sequence by the incorporation of a positively charged amino acid could modulate the zipper-like structure into a functional DNA-binding module
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