Abstract
Collagen, the most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration. The Gly-Pro-Hyp canonical tripeptide repeating unit of the collagen superhelix has been well-characterized. However, to date, the shortest tripeptide repeat demonstrated to attain a helical conformation contained 3–10 peptide repeats. Here, taking a minimalistic approach, we studied a single repeating unit of collagen in its protected form, Fmoc-Gly-Pro-Hyp. The peptide formed single crystals displaying left-handed polyproline II superhelical packing, as in the native collagen single strand. The crystalline assemblies also display head-to-tail H-bond interactions and an “aromatic zipper” arrangement at the molecular interface. The coassembly of this tripeptide, with Fmoc-Phe-Phe, a well-studied dipeptide hydrogelator, produced twisted helical fibrils with a polyproline II conformation and improved hydrogel mechanical rigidity. The design of these peptides illustrates the possibility to assemble superhelical nanostructures from minimal collagen-inspired peptides with their potential use as functional motifs to introduce a polyproline II conformation into hybrid hydrogel assemblies.
Highlights
Collagen, the most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration
The torsion angles calculated around the Fmoc-Gly peptide residue gave values for the φ1 and ψ1 angles of −69.21 and +136.24°, followed by −66.2 and +150.3° for the Gly-Pro residue (Figure 1a). These results suggest the presence of a aSchematic illustration of the structural design of a collagenmimicking minimal tripeptide and its coassembly to form a rigid hydrogel with a twisted architecture showing (1) collagen triplehelix, (2) tripeptide repeating sequence in each strand of the triple helix, (3) minimal repeating sequence Gly-Pro-Hyp in a collagen helix, (4) a single crystal unit of Fmoc-modified Gly-Pro-Hyp revealing the presence of a polyproline helix II conformation, (5) Fmoc-Phe-Phe, the rigid hydrogelator, coassembled with Fmoc-Gly-Pro-Hyp, (6) development of a coassembled hybrid hydrogel, Fmoc-PhePhe:Fmoc-Gly-Pro-Hyp, displaying a polyproline helix II conformation and twisted helical fibrils
We have recently demonstrated the ability of various Fmoc-protected amino acids and biopolymers to coassemble with Fmoc-Phe-Phe to produce hybrid hydrogels with adjustable mechanical properties and with higher stability and better biofunctionality than any of the individual component building blocks.[25,26,41−44] Motivated by our previous work, here, we coassembled the Fmoc-Gly-Pro-Hyp peptide with Fmoc-Phe-Phe to form a hydrogel that combines the properties of the two peptides (Scheme 1)
Summary
The most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration. The crystalline assemblies display head-to-tail H-bond interactions and an “aromatic zipper” arrangement at the molecular interface The coassembly of this tripeptide, with Fmoc-Phe-Phe, a well-studied dipeptide hydrogelator, produced twisted helical fibrils with a polyproline II conformation and improved hydrogel mechanical rigidity. Protein and peptide-based hydrogels possess unique biofunctionality, biocompatibility, and biodegradability that make them suitable for a wide range of applications Among others, these include their use as scaffolds, for wound healing and tissue engineering, encapsulation and slow release of drugs and biomolecules, serving as templates for nanofabrication, and as catalysts for organic reactions.[15−21] A prominent example is fluorenylmethoxycarbonyl-Phe-Phe (Fmoc-Phe-Phe), which forms a rigid biocompatible self-assembled scaffold, consisting of a fibrous network that is stable across a broad range of pH conditions and temperatures.[22,23] coassembly of two different building blocks into one ordered structure demonstrated improvements in the mechanical properties, stability, and biofunctionality as compared to hydrogels assembled from each of the individual components.[24−31]. These findings can be utilized to develop potential structural biomaterials with desirable properties
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