Catalytic Efficiency of Chitinase-D on Insoluble Chitinous Substrates Was Improved by Fusing Auxiliary Domains

Chitin is an abundant renewable polysaccharide, next only to cellulose. Chitinases are important for effective utilization of this biopolymer. Chitinase D from Serratia proteamaculans ( Sp ChiD) is a single domain chitinase with both hydrolytic and transglycosylation (TG) activities. Sp ChiD had less of hydrolytic activity on insoluble polymeric chitin substrates due to the absence of auxiliary binding domains. We improved catalytic efficiency of Sp ChiD in degradation of insoluble chitin substrates by fusing with auxiliary domains like polycystic kidney disease (PKD) domain and chitin binding protein 21 (CBP21). Of the six different Sp ChiD fusion chimeras, two C-terminal fusions viz. ChiD+PKD and ChiD+CBP resulted in improved hydrolytic activity on α- and β-chitin, respectively. Time-course degradation of colloidal chitin also confirmed that these two C-terminal Sp ChiD fusion chimeras were more active than other chimeras. More TG products were produced for a longer duration by the fusion chimeras ChiD+PKD and PKD+ChiD+CBP.