Xuehua Pan, Jinping Lei, Xuhui Huang and Yanxiang Zhao
Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong
β-lactamases are a large family of bacterial enzymes that hydrolyze and inactivate clinically used β-lactam antibiotics through a catalytic process mediated by either a serine residue (Class A, C and D) or a metal ion (Class B). With such catalytic prowess, β-lactamases confer antibiotic resistance to bacteria strains that express these enzymes either from a chromosome site or by a transmittable plasmid. There is great interest in understanding the molecular mechanism of these enzymes because such information would enable the development of novel antibiotics and β-lactamase-specific inhibitors. While extensive amount of information has been accumulated over the past decades that elucidates the biochemical and molecular details of the catalytic process, certain aspects of the catalytic cycle are still not fully understood, partly due to the ultrafast kinetics observed in these enzymes that renders "trapping" and investigating a functional intermediate technically challenging. Using mutational perturbation, our lab has generated a series of Class A β-lactamase mutants with significantly slowed enzymatic kinetics. Using these mutants as "surrogates", we managed to track a full cycle of catalysis using time-resolved protein crystallography. These studies have provided novel insights into the functional mechanism of these bacterial enzymes. For example, our studies have uncovered novel conformational changes within the active site that occur in sync with distinct catalytic steps. Our structures of functional intermediates along the catalytic pathway suggest alternative intermediate states. In summary, our structural studies improves our understanding of β-lactamase-mediated antibiotic resistance and can potentially support drug discovery effect to identify novel antimicrobial agents.
Keywords: β lactamase, antibiotic resistance, catalysis.