Antibiotic Recognition by Binuclear Metallo-β-Lactamases Revealed by X-ray Crystallography

Publisher Website
Google Scholar
Abstract
Metallo-β-lactamases are zinc-dependent enzymes responsible for resistance to β-lactam antibiotics in a variety of host bacteria, usually Gram-negative species that act as opportunist pathogens. They hydrolyze all classes of β-lactam antibiotics, including carbapenems, and escape the action of available β-lactamase inhibitors. Efforts to develop effective inhibitors have been hampered by the lack of structural information regarding how these enzymes recognize and turn over β-lactam substrates. We report here the crystal structure of the Stenotrophomonas maltophilia L1 enzyme in complex with the hydrolysis product of the 7α-methoxyoxacephem, moxalactam. The on-enzyme complex is a 3‘-exo-methylene species generated by elimination of the 1-methyltetrazolyl-5-thiolate anion from the 3‘-methyl group. Moxalactam binding to L1 involves direct interaction of the two active site zinc ions with the β-lactam amide and C4 carboxylate, groups that are common to all β-lactam substrates. The 7β-[(4-hydroxyphenyl)malonyl]-amino substituent makes limited hydrophobic and hydrogen bonding contacts with the active site groove. The mode of binding provides strong evidence that a water molecule situated between the two metal ions is the most likely nucleophile in the hydrolytic reaction. These data suggest a reaction mechanism for metallo-β-lactamases in which both metal ions contribute to catalysis by activating the bridging water/hydroxide nucleophile, polarizing the substrate amide bond for attack and stabilizing anionic nitrogen intermediates. The structure illustrates how a binuclear zinc site confers upon metallo-β-lactamases the ability both to recognize and efficiently hydrolyze a wide variety of β-lactam substrates.

This publication has 36 references indexed in Scilit: