Overexpression, Purification, and Characterization of the Cloned Metallo-β-Lactamase L1 from Stenotrophomonas maltophilia

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Abstract
The metallo-β-lactamase L1 from Stenotrophomonas maltophilia was cloned, overexpressed, and characterized by spectrometric and biochemical techniques. Results of metal analyses were consistent with the cloned enzyme having 2 mol of tightly bound Zn(II) per monomer. Gel filtration chromatography demonstrated that the cloned enzyme exists as a tightly held tetramer with a molecular mass of ca. 115 kDa, and matrix-assisted laser desorption ionization and time-of-flight mass spectrometry indicated a monomeric molecular mass of 28.8 kDa. Steady-state kinetic studies with a number of diverse penicillin and cephalosporin antibiotics demonstrated that L1 effectively hydrolyzes all tested compounds, withkcat/Km values ranging between 0.002 and 5.5 μM−1 s−1. These characteristics of the recombinant enzyme are contrasted to those previously reported for metallo-β-lactamases isolated directly fromS. maltophilia.