Mutational analysis to identify the residues essential for the acetyltransferase activity of GlmU in Bacillus subtilis

Abstract

The novel and attractive antimicrobial drug target, glucosamine-1-phosphate acetyltransferase/N-acetylglucosamine-1-phosphate uridyltransferase (GlmU), is a bifunctional enzyme that catalyzes two sequential steps in the biosynthesis of UDP-GlcNAc, essential for both lipopolysaccharide and peptidoglycan in Gram positive and Gram negative bacteria. Glucosamine-1-phosphate acetyltransferase catalyzes the formation of N-acetylglucosamine-1-phosphate and N-acetylglucosamine-1-phosphate uridylyltransferase catalyzes the formation of UDP-GlcNAc. In this study, glmU genes from Escherichia coli and Bacillus subtilis were cloned and the corresponding proteins were produced in an E. coli BL21 (DE3) expression system. The kinetic parameters and reaction conditions, such as initial reaction rate, optimal temperature and pH, and the effect of Mg²⁺ ion concentration of GlmU enzymes from E. coli (Ec-GlmU) and B. subtilis (Bs-GlmU) were detected. Compared to Ec-GlmU, Bs-GlmU exhibits much lower glucosamine-1-phosphate acetyltransferase activity. Based on the in silico results of a virtual amino acid mutation and molecular docking of Bs-GlmU, five mutants were successfully constructed to verify the predicted alterations of acetyltransferase activity. The result of point mutations indicated that the C405 and A380 residues played key role in catalytic mechanism of acetyltransferase of Bs-GlmU providing new insight into the reaction mechanism of GlmU enzymes and supporting the further development of antimicrobial drugs.