Enzymatic and Structural Characterization of Alanine Racemase from Enterococcus faecium by Kinetic and Computational Studies

Abstract

The surge in vancomycin-resistant enterococci (VRE) strains poses a serious threat to public and clinical health. VRE strains are the leading cause of multi-drug resistant enterococcal infections and are commonly acquired from medical devices. Therefore, it is essential to discover new antibacterial targets and drugs for this pathogen. Alanine racemase could be a valuable drug target due to its crucial role in E. faecium survival. Alr from E. faecium (EF_Alr) was heterologously produced and purified from E. coli., and the steady-state kinetic constants were determined at different pH values. Using a coupled reaction with L-alanine dehydrogenase, rate of production of NADH was measured at 340 nm to observe EF_Alr activity in the D- to L-alanine direction. The highest catalytic efficiency, 8.61 ± 0.5 s-1 mM-1, was found at pH 9. Additionally, the tentative active site residues, Lys40 and Tyr268, for the alanine racemization reaction were assigned by homology modeling and sequence comparison studies. Using UCSF Chimera, the structure of the EF_Alr homology model was superimposed and compared to the crystal structure of Alr from E. faecalis. KEYWORDS: Alanine Racemase; Enterococcus faecium; Vancomycin-Resistant Enterococci; Homology Modeling; pH Optimum; Kinetic Characterization; SWISS-MODEL Server; Steady-State Kinetics