Grafting of tyrosine-containing peptide onto silk fibroin membrane for improving enzymatic reactivity

Abstract

During enzymatic modifications of silk fibroins, the accessibility of tyrosinases to the reactive sites was limited owing to the steric hindrance of tyrosine residues in the fibroin proteins. To improve the reactivity of silk fibroin, a tyrosine-containing peptide (TyrP) was covalently grafted onto the fibroin surfaces using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Enzymatic oxidation of the modified fibroins was subsequently carried out with a mushroom tyrosinase, followed by coupling of e-polylysine (e-PL) with the generated o-quinone residues of silk fibroins. The efficacy of grafting reaction was examined by means of SDS-PAGE and amine acid analysis. The results indicated EDC treatment might cause the direct self-crosslinks of silk fibroins and TyrP-bridged cross-links of fibroin molecules as well, which led to a noticeable increase in the molecular weight of fibroin proteins. TyrP-grafted fibroins displayed higher reactivity compared to the untreated, and more e-PL was bonded to the fibroin surfaces when incubating with tyrosinase, resulting in improved wettability and mechanical property. The presented work offers an efficient alternative for the enzymatic modification of the fibroin-based materials with tyrosinase.