title: Inhibition of TEM-2 beta-lactamase from Escherichia coli by clavulanic acid: observation of intermediates by electrospray ionization mass spectrometry.
abstract: Clavulanic acid, the therapeutically important inhibitor of beta-lactamases containing a nucleophilic serine residue at their active sites, inhibits Escherichia coli TEM-2 beta-lactamase via a complex mechanism. Electrospray ionization mass spectrometry (ESIMS) studies revealed that a minimum of four different modified proteins are formed upon incubation of clavulanate with the TEM-2 enzyme. These exhibit mass increments relative to the unmodified TEM-2 beta-lactamase of 52, 70, 88, and 155 Da. Time course studies implied that no long-lived forms of clavulanate-inhibited TEM-2 beta-lactamase retain the carbons of the oxazolidine ring of clavulanate. The absence of a 199 Da increment to unmodified TEM-2 suggests rapid decarboxylation of clavulanate upon binding to the enzyme. Proteolytic digestions of purified forms of clavulanate inhibited TEM-2 beta-lactamase followed by analyses using high-performance liquid chromatography coupled to ESIMS (HPLC-ESIMS) and chemical sequencing were used to provide positional information on the modifications to the enzyme. Increments of 70 and 80 Da increments were shown to be located in a peptide containing Ser-70. A further 70 Da mass increment, assigned as a beta-linked acrylate, was localized to a peptide containing Ser-130. A mechanistic scheme for the reaction of clavulanate with TEM-2 beta-lactamase is proposed in which acylation at Ser-70 and subsequent decarboxylation is followed either by cross-linking with Ser-130 to form a vinyl ether or by reformation of unmodified enzyme via a Ser-70 linked (hydrated) aldehyde. Purified cross-linked vinyl ether was observed to slowly convert under acidic conditions to a Ser-70 linked (hydrated) aldehyde with concomitant conversion of Ser-130 to a dehydroalanyl residue.
authors.affiliation: Dyson Perrins Laboratory, Oxford, UK.
authors.forename: R P
authors.initials: RP
authors.lastname: Brown
authors.forename: R T
authors.initials: RT
authors.lastname: Aplin
authors.forename: C J
authors.initials: CJ
authors.lastname: Schofield
mesh_terms: D019818:Clavulanic Acid; D002969:Clavulanic Acids / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004229:Dithiothreitol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D013058:Mass Spectrometry; D008956:Models, Chemical; D015394:Molecular Structure; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D012694:Serine / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism
chemical_list: D002969:Clavulanic Acids; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid; D012694:Serine; D010397:Penicillanic Acid; C031528:6-iodopenicillanic acid; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D014357:Trypsin; D001618:beta-Lactamases; C056342:beta-lactamase TEM-2; D004229:Dithiothreitol