2qjs
|
Stenotrophomonas maltophilia L1 metallo-beta-lactamase Asp-120 Asn mutant
OverviewOverview
Metallo-beta-lactamases (mbetals) are zinc-dependent enzymes that, hydrolyze a wide range of beta-lactam antibiotics. The mbetal active site, features an invariant Asp-120 that ligates one of the two metal ions (Zn2), and a metal-bridging water/hydroxide (Wat1). Previous studies show that, substitutions at Asp-120 dramatically affect mbetal activity, but no, consensus exists as to its role in beta-lactam turnover. Here we present, crystal structures of the Asn and Cys mutants of Asp-120 of the L1 mbetal, from Stenotrophomonas maltophilia. Both mutants retain a dinuclear zinc, center with Wat1 present. In the essentially inactive Cys enzyme Zn2 is, displaced to a more buried position relative to that in the wild-type, enzyme. In the catalytically impaired Asn enzyme the coordination of Zn2, is altered, neither it nor Wat1 is coordinated by Asn-120, and the, N-terminal 19 amino acids, important to cooperative interactions between, subunits in the wild-type enzyme, are disordered. Comparison with the, structure of L1 complexed with the hydrolyzed oxacephem moxalactam, suggests that in the Cys mutant Zn2 can no longer make stabilizing, interactions with anionic nitrogen species formed in the hydrolytic, reaction. The diminished activity of the Asn mutant arises from a, combination of loss of intersubunit interactions and impaired proton, transfer to, and reduced interaction of Zn2 with, the substrate amide, nitrogen. We conclude that, while interactions of Asp-120 with active site, water molecules are important to proton transfer and possibly nucleophilic, attack by Wat1, its primary role is to optimally position Zn2 for, catalytically important interactions with the charged amide nitrogen of, substrate.
About this StructureAbout this Structure
2QJS is a Single protein structure of sequence from Stenotrophomonas maltophilia with ZN as ligand. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
ReferenceReference
Structural Basis for the Role of Asp-120 in Metallo-beta-lactamases(,)., Crisp J, Conners R, Garrity JD, Carenbauer AL, Crowder MW, Spencer J, Biochemistry. 2007 Sep 18;46(37):10664-10674. Epub 2007 Aug 23. PMID:17715946
Page seeded by OCA on Wed Nov 21 13:52:07 2007