Synthesis of Enzymatically Crosslinkable Peptide‐Poly( L ‐lysine) Conjugate and Creation of Bio‐Inspired Hybrid Fibers

Summary: Poly( L ‐lysine)s having an N ε ‐substituted tetrapeptide, Lys‐Gly‐Tyr‐Gly, were synthesized by the coupling of the protected tetrapeptide active ester, Boc‐Lys(Z)‐Gly‐Tyr(Bzl)‐Gly (4‐hydroxyphenyl)dimethylsulfonium methylsulfate and N ε ‐group of the poly( L ‐lysine) side chain. The N ε ‐substituted tetrapeptide functions as the substrate of tyrosinase and is responsible for the enzyme‐mediated interpolymer cross‐linking. The degree of N ε ‐substitution (DS) was mostly controlled by changing the stoichiometry between the N ε ‐amino groups of the parent poly( L ‐lysine) and the protected tetrapeptide active ester. Two kinds of samples having DS values of 8.6 and 18 mol‐% were prepared. The resulting cationic N ε ‐(Lys‐Gly‐Tyr‐Gly)‐poly( L ‐lysine) (abbreviated as PLL(GYGK)) was spun into hybrid fibers with the anionic polysaccharide gellan via a polyionic complexation reaction at the interface between aqueous solutions of the two polymers. The mechanical strengths of the PLL(GYGK)‐gellan hybrid fibers were superior to those of the original poly( L ‐lysine)‐gellan fibers. The mechanical strength of the hybrid fibers further increased upon the tyrosinase‐mediated cross‐linking reaction of the PLL(GYGK). This result indicates that the covalent cross‐bridge formation between the N ε ‐substituted peptides significantly contributed to reinforcement of the hybrid fibers. The present study affords a new methodology for reinforcement inspired by a biological process.Reinforcement mechanism of the PLL(GYGK)‐gellan hybrid fiber.