Collagen-Inspired Helical Peptide Coassembly Forms a Rigid Hydrogel with Twisted Polyproline II Architecture

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.

胶原蛋白（Collagen）是哺乳动物体内含量最为丰富的蛋白质，兼具优异的黏合性与弹性，可高效诱导组织再生。胶原蛋白超螺旋的典型三肽重复单元为甘氨酸-脯氨酸-羟脯氨酸（Gly-Pro-Hyp），该序列已被充分表征。然而截至目前，已被证实能够形成螺旋构象的最短三肽重复序列包含3~10个肽重复单元。本研究采用极简研究策略，对保护形式的单胶原蛋白重复单元Fmoc-甘氨酸-脯氨酸-羟脯氨酸（Fmoc-Gly-Pro-Hyp）开展了研究。该肽可形成单晶体，呈现出与天然胶原蛋白单链一致的左手聚脯氨酸II型超螺旋堆积结构。其晶体组装体还存在首尾氢键相互作用，并在分子界面处形成“芳香拉链”排布。将该三肽与已被广泛研究的二肽凝胶因子Fmoc-苯丙氨酸-苯丙氨酸（Fmoc-Phe-Phe）进行共组装，可得到具有聚脯氨酸II型构象的扭曲螺旋原纤维，且水凝胶的机械刚度得以提升。此类肽的设计方案证明，可从极简的胶原蛋白仿生肽中组装出超螺旋纳米结构，这类肽有望作为功能性基元，将聚脯氨酸II型构象引入杂合水凝胶组装体中。