Orthogonal Enzymatic Conjugation Reactions Create Chitin Binding Domain Grafted Chitinase Polymers with Enhanced Antifungal Activity.

Enzymatic reaction offers site-specific conjugation of protein units to form protein conjugates or protein polymers with intrinsic functions. Herein, we report horseradish peroxidase (HRP)- and microbial transglutaminase (MTG)-catalyzed orthogonal conjugation reactions to create antifungal protein polymers composed of chitinase-A (ChiA) and its two domains, catalytic domain, CatD, and chitin-binding domain, LysM. We engineered the ChiA and CatD by introducing a peptide tag containing tyrosine (Y-tag) at N-termini and a peptide tag containing lysine and tyrosine (KY-tag) at C-termini to construct Y-ChiA-KY and Y-CatD-KY. Also, LysM with Y-tag and KY-tag (Y-LysM-KY) or with a glutamine-containing peptide tag (Q-tag) (LysM-Q) were constructed. The proteins with Y-tag and KY-tag were efficiently polymerized by HRP reaction through the formation of dityrosine bonds at the tyrosine residues in the peptide tags. The Y-CatD-KY polymer was further treated by MTG to orthogonally graft LysM-Q to the KY-tag via isopeptide formation between the side chains of the glutamine and lysine residues in the peptide tags to form LysM-grafted CatD polymer. The LysM-grafted CatD polymer exhibited significantly higher antifungal activity than the homopolymer of Y-ChiA-KY and the random copolymer of Y-CatD-KY and Y-LysM-KY, demonstrating that the structural differences of artificial chitinase polymers have a significant impact on the antifungal activity. This strategy of polymerization and grafting reaction of protein can contribute to the further research and development of functional protein polymers for specific applications in various fields in biotechnology.