title: Inhibition of serine beta-lactamases by vanadate-catechol complexes.
abstract: All three classes of serine beta-lactamases are inhibited at micromolar levels by 1:1 complexes of catechols with vanadate. Vanadate reacts with catechols at submillimolar concentrations in aqueous buffer at neutral pH in several steps, initially forming 1:1, 1:2, and, possibly, 1:3 complexes. Formation of these complexes is followed by the slower reduction of vanadate (V (V)) to vanadyl (V (IV)) and oxidation of the catechol. Vanadyl-catechol complexes, however, do not inhibit the beta-lactamases. Rate and equilibrium constants of formation of the 1:1 and 1:2 complexes of vanadate with catechol itself and with 2,3-dihydroxynaphthalene were measured by stopped-flow spectrophotometry. Typical examples of all three classes of serine beta-lactamases (the class A TEM-2, class C P99, and class D OXA-1 enzymes) were competitively inhibited by the 1:1 vanadate-catechol complexes. The inhibition was modestly enhanced by hydrophobic substituents on the catechol. The 1:1 vanadate complexes are considerably better inhibitors of the P99 beta-lactamase than 1:1 complexes of catechol with boric acid and are likely to contain penta- or hexacoordinated vanadium rather than tetracooordinated. Molecular modeling showed that a pentacoordinated 1:1 vanadate-catechol complex readily fits into the class C beta-lactamase active site with coordination to the nucleophilic serine hydroxyl oxygen. Such complexes may resemble the pentacoordinated transition states of phosphyl transfer, a reaction also catalyzed by beta-lactamases.
authors.affiliation: Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Adediran
authors.forename: R F
authors.initials: RF
authors.lastname: Pratt
mesh_terms: D001426:Bacterial Proteins; D002396:Catechols / Q000737:chemistry*; D016972:Enterobacter cloacae / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D010084:Oxidation-Reduction; D014638:Vanadates / Q000737:chemistry*; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002396:Catechols; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D014638:Vanadates; D001618:beta-Lactamases