ja405319n_si_001.pdf (1.57 MB)
Mechanism of Acyl–Enzyme Complex Formation from the Henry–Michaelis Complex of Class C β‑Lactamases with β‑Lactam Antibiotics
journal contribution
posted on 2016-02-18, 18:54 authored by Ravi Tripathi, Nisanth N. NairBacteria that cause most of the hospital-acquired
infections make
use of class C β-lactamase (CBL) among other enzymes to resist
a wide spectrum of modern antibiotics and pose a major public health
concern. Other than the general features, details of the defensive
mechanism by CBL, leading to the hydrolysis of drug molecules, remain
a matter of debate, in particular the identification of the general
base and role of the active site residues and substrate. In an attempt
to unravel the detailed molecular mechanism, we carried out extensive
hybrid quantum mechanical/molecular mechanical Car–Parrinello
molecular dynamics simulation of the reaction with the aid of the
metadynamics technique. On this basis, we report here the mechanism
of the formation of the acyl–enzyme complex from the Henry–Michaelis
complex formed by β-lactam antibiotics and CBL. We considered
two β-lactam antibiotics, namely, cephalothin and aztreonam,
belonging to two different subfamilies. A general mechanism for the
formation of a β-lactam antibiotic–CBL acyl–enzyme
complex is elicited, and the individual roles of the active site residues
and substrate are probed. The general base in the acylation step has
been identified as Lys67, while Tyr150 aids
the protonation of the β-lactam nitrogen through either the
substrate carboxylate group or a water molecule.