Metallo-β-lactamases (MBLs) are the major group of carbapenemases produced by bacterial pathogens. The design of MBL inhibitors has been limited by, among other issues, incomplete knowledge about how these enzymes modulate substrate recognition. While most MBLs are broad-spectrum enzymes, B2 MBLs are exclusive carbapenemases. This narrower substrate profile has been attributed to a sequence insertion present in B2 enzymes that limits accessibility to the active site. In this work, we evaluate the role of sequence insertions naturally occurring in the B2 enzyme Sfh-I and in the broad-spectrum B1 enzyme SPM-1. We engineered a chimeric protein in which the sequence insertion of SPM-1 was replaced by the one present in Sfh-I. The chimeric variant is a selective cephalosporinase, revealing that the substrate profile of MBLs can be further tuned depending on the protein context. These results also show that the stable scaffold of MBLs allows a modular engineering much richer than the one observed in nature.
The reactivity of the Cu(II) complex of N,N'-bis(pyridin-2-ylmethylene)propane-1,3-diamine (py 2 pn), [Cu(py 2 pn)(ClO 4 ) 2 ], toward O 2and H 2 O 2 has been examined. The complex reacts with O 2 *À with fast second order kinetics, k McF = 4.05 × 10 6 M À 1 s À 1 , employing the Cu(II)/Cu(I) couple proved by spectroscopic detection of the reduced form at low temperature. At À 40 °C in DMF, the reaction of the complex with H 2 O 2 /Et 3 N yields an stable end-on Cu(II)-hydroperoxide, with k OOH = 0.31 min À 1 , the formation of which has been established by DFT calculations, electronic and EPR spectra. At room temperature, the end-on Cu(II)-hydroperoxide reacts with a second Cu(II) complex to evolve O 2 , with k CAT = 83.2 M À 2 s À 1 . The Cu(II)-hydroperoxide can mediate phenol oxidation, probably through a trigonal bipyramidal ternary transition state based on DFT analysis, favored over catalase activity when low proportion of catalyst is used. In these reactions, structural constraints imposed by the ligand distort the coordination geometry of the metal and controls reactivity.
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