Interactions of Oximino-Substituted Boronic Acids and beta-Lactams with the CMY-2-Derived Extended-Spectrum Cephalosporinases CMY-30 and CMY-42
CMY-30 and CMY-42 are extended-spectrum (ES) derivatives of CMY-2. ES characteristics are due to substitutions of Gly (CMY-30) and Ser (CMY-42) for Val211 in the Omega-loop. To characterize the effects of 211 substitutions, we studied the interactions of CMY-2, -30, and -42 with boronic acid transition state inhibitors (BATSIs) resembling ceftazidime and cefotaxime, assessed thermal stability of the enzymes in their free forms and in complexes with BATSIs and oximino-beta-lactams, and simulated, using molecular dynamics (MD), the CMY-42 apoenzyme and the CMY-42 complexes with ceftazidime and the ceftazidime-like BATSI. Inhibition constants showed that affinities between CMY-30 and CMY-42 and the R1 groups of BATSIs were lower than those of CMY-2. ES variants also exhibited decreased thermal stability either as apoenzymes or in covalent complexes with oximino compounds. MD simulations further supported destabilization of the ES variants. Val211Ser increased thermal factors of the Omega-loop backbone atoms, as previously observed for CMY-30. The similar effects of the two substitutions seemed to be due to a less-constrained Tyr221 likely inducing concerted movement of elements at the edges of the active site (Omega-loop-Q120 loop-R2 loop/H10 helix). This inner-protein movement, along with the wider R1 binding cleft, enabled intense vibrations of the covalently bound ceftazidime and ceftazidime-like BATSIs. Increased flexibility of the ES enzymes may assist the productive adaptation of the active site to the various geometries of the oximino substrates during the reaction (higher frequency of near-attack conformations).