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Metallo-β-lactamases catalyze the hydrolysis of most β-lactam antibiotics and hence represent a major clinical concern. The development of inhibitors for these enzymes is complicated by the diversity and flexibility of their substrate-binding sites, motivating research into their structure and function. In this study, we examined the conformational properties of the Bacillus cereus β-lactamase II in the presence of chemical denaturants using a variety of biochemical and biophysical techniques. The apoenzyme was found to unfold cooperatively, with a Gibbs free energy of stabilization (ΔG(0)) of 32 ± 2 kJ·mol(-1) For holoBcII, a first non-cooperative transition leads to multiple interconverting native-like states, in which both zinc atoms remain bound in an apparently unaltered active site, and the protein displays a well organized compact hydrophobic core with structural changes confined to the enzyme surface, but with no catalytic activity. Two-dimensional NMR data revealed that the loss of activity occurs concomitantly with perturbations in two loops that border the enzyme active site. A second cooperative transition, corresponding to global unfolding, is observed at higher denaturant concentrations, with ΔG(0) value of 65 ± 1.4 kJ·mol(-1) These combined data highlight the importance of the two zinc ions in maintaining structure as well as a relatively well defined conformation for both active site loops to maintain enzymatic activity.

Original publication

DOI

10.1074/jbc.M116.719005

Type

Journal article

Journal

J Biol Chem

Publication Date

29/07/2016

Volume

291

Pages

16124 - 16137

Keywords

antibiotic resistance, circular dichroism (CD), enzyme catalysis, metalloenzyme, nuclear magnetic resonance (NMR), protein folding, zinc, β-lactamase, Bacillus cereus, Catalytic Domain, Hydrophobic and Hydrophilic Interactions, Protein Structure, Secondary, Protein Unfolding, Zinc, beta-Lactamases