Thermostability enhancement of chitosanase CsnA by fusion a family 5 carbohydrate-binding module

To determine the effects of carbohydrate-binding modules (CBMs) on the thermostability and catalytic efficiency of chitosanase CsnA. Three CBMs (BgCBM5, PfCBM32-2 and AoCBM35) were engineered at the C-terminus of chitosanase CsnA to create hybrid enzymes CsnA-CBM5, CsnA-CBM32 and CsnA-CBM35. K (m) values of all the hybrid enzymes were lower than that of the wild type (WT) enzyme; however, only CsnA-CBM5 had an elevated specific activity and catalytic efficiency. The fusion of BgCBM5 enhanced the thermostability of the enzyme, which exhibited a 8.9 A degrees C higher T-50 and a 2.9 A degrees C higher T-m than the WT. Secondary structural analysis indicated that appending BgCBM5 at the C-terminus considerably changed the secondary structure content. The fusion of BgCBM5 improved the thermal stability of CsnA, and the obtained hybrid enzyme (CsnA-CBM5) is a useful candidate for industrial application.