Characterisation of monomeric L1 metallo-beata-lactamase and the role of the N-terminal extension in negative cooperativity and antibiotic hydrolysis

AM Simm, CS Higgins, AL Carenbauer, MW Crowder, JH Bateson, PM Bennett, AR Clarke, SE Halford, TR Walsh

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

The L1 metallo-beta-lactamase from Stenotrophomonas maltophilia is unique among this class of enzymes because it is tetrameric. Previous work predicted that the two regions of important intersubunit interaction were the residue Met-140 and the N-terminal extensions of each subunit. The N-terminal extension was also implicated in beta-lactam binding. Mutation of methionine 140 to aspartic acid results in a monomeric L1 beta-lactamase with a greatly altered substrate specificity profile. A 20-amino acid N-terminal deletion mutant enzyme (N-Del) could be isolated in a tetrameric form but demonstrated greatly reduced rates of beta-lactam hydrolysis and different substrate profiles compared with that of the parent enzyme. Specific site-directed mutations of individual N terminus residues were made (Y11S, W17S, and a double mutant L5A/L8A). All N-terminal mutant enzymes were tetramers and all showed higher K(m) values for ampicillin and nitrocefin, hydrolyzed ceftazidime poorly, and hydrolyzed imipenem more efficiently than ampicillin in contrast to wild-type L1. Nitrocefin turnover was significantly increased, probably because of an increased rate of breakdown of the intermediate species due to a lack of stabilizing forces. K(m) values for monomeric L1 were greatly increased for all antibiotics tested. A model of a highly mobile N-terminal extension in the monomeric enzyme is proposed to explain these findings. Tetrameric L1 shows negative cooperativity, which is not present in either the monomer or N-terminal deletion enzymes, suggesting that the cooperative effect is mediated via N-terminal intersubunit interactions. These data indicate that while the N terminus of L1 is not essential for beta-lactam hydrolysis, it is clearly important to its activity and substrate specificity.
Translated title of the contributionCharacterisation of monomeric L1 metallo-beata-lactamase and the role of the N-terminal extension in negative cooperativity and antibiotic hydrolysis
Original languageEnglish
Pages (from-to)24744 - 24752
Number of pages9
JournalJournal of Biological Chemistry
Volume277
Publication statusPublished - Jul 2002

Bibliographical note

Publisher: The American Society for Biochemistry and Molecular Biology, Inc

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