Enhancement reactivity of Bombyx mori silk fibroins via genipin-mediated grafting of a tyrosine-rich polypeptide

Bombyx mori silk fibroin has potential applications in the biomedical field owing to its satisfactory biocompatibility. In the present work, a tyrosine-rich polypeptide (P) with the sequence of GKGYGGYGK was grafted onto fibroin molecules using a natural cross-linking agent of genipin (GP), aiming at improving the reactivity of the fibroin-based materials. Incubation of the polypeptide-grafted fibroin membrane was subsequently carried out, with a mushroom tyrosinase (MT) and a model functional macromolecule of ε-poly-l-lysine (ε-PL). The changes in the structure and composition of the silk fibroin before and after polypeptide grafting were examined by means of size exclusion chromatography and amino acid analysis. The results indicated that the polypeptide was covalently bonded to fibroin chains and evidently promoted the succeeding enzymatic coupling of ε-PL with fibroins, resulting in a higher content of ε-PL compared to the control. The obtained antibacterial activities against S. aureus and E. coli for the fibroin membrane treated with GP/P and MT/ε-PL was more satisfactory than others. Cytotoxicity testing reveals that polypeptide grafting did less impact on the biocompatibility of silk fibroins. The present work provides a novel method to improve the reactivity of silk fibroins and it can be utilized for bio-functionalization of silk fibroin.