Engineering the Relatively Conserved Residues in Active Site Architecture of Thermophilic Chitinase SsChi18A Enhanced Catalytic Activity

Chitinase plays a vital role in the efficient biotransformation of the chitin substrate. This study aimed to modify and elucidate the contribution of the relatively conserved residues in the active site architecture of a thermophilic chitinase SsChi18A from Streptomyces sp. F-3 in processive catalysis. The enzymatic activity on colloidal chitin increased to 151%, 135%, and 129% in variants Y286W, E287A, and K186A compared with the wild type (WT). Also, the apparent processive parameter G2/G1 was lower in the variants compared to the WT, indicating the essential role of Tyr-286, Glu-287, and Lys-186 in processive catalysis. Additionally, the enzymatic activity on the crystalline chitin of F48W and double mutants F48W/Y209F and F48W/Y286W increased by 35%, 16%, and 36% compared with that for WT. Molecular dynamics simulations revealed that the driving force of processive catalysis might be related to the changes in interaction energy. This study provided a rational design strategy targeting relatively conserved residues to enhance the catalytic activity of GH18 processive chitinases.