Functional and structural characterization of Staphylococcus aureus N-acetylglucosamine 1-phosphate uridyltransferase (GlmU) reveals a redox-sensitive acetyltransferase activity.

Abstract

The bifunctional enzyme N-acetylglucosamine 1-phosphate uridyltransferase (GlmU) is a promising antibiotic drug target, as it facilitates the biosynthesis of uridine 5'-diphospho-N-acetylglucosamine, an essential precursor of cell wall constituents. We identified that Staphylococcus aureus GlmU (SaGlmU), which was previously targeted for inhibitor development, possesses a dual-cysteine variation (C379/C404) within the acetyltransferase active site. Enzyme assays performed under reducing and non-reducing conditions revealed that the acetyltransferase activity of SaGlmU is redox-sensitive, displaying ~15-fold lower turnover and ~3-fold higher K_M value for the acetyl CoA substrate under non-reducing conditions. This sensitivity was absent in a C379A SaGlmU mutant. Analysis of SaGlmU by mass spectrometry, x-ray crystallography, and in silico modeling support that C379 and C404 act as a reversible, redox-sensitive switch by forming a disulfide under non-reducing conditions that impedes acetyl CoA recognition and turnover. Therefore, we recommend that future in vitro screening and characterization of SaGlmU inhibitors consider both reducing and non-reducing conditions.