PURIFICATION OF STAPHYLOCOCCUS-AUREUS BETA-LACTAMASES BY USING SEQUENTIAL CATION-EXCHANGE AND AFFINITY-CHROMATOGRAPHY

Boronic acids are active-site inhibitors of serine β-lactamases, and a phenylboronic acid-agarose affinity column has been used to purify β-lactamase from crude cell extracts of several bacterial species. We applied phenylboronic acid-agarose chromatography to the purification of Staphylococcus aureus β-lactamase. Two factors interfered with the succes of the previously described single-step chromatographic protocol. First, staphylococcal β-lactamase exhibited non-active-site-mediated adsorption to the agarose used as a support for the meta-aminophenylborate ligand, preventing the recovery of β-lactamase from the column. Second, the staphylococcal β-lactamases exhibited low affinity for meta-aminophenylborate with inhibition constants (K(i)s) ranging from 8.0 x 10-3 to 20.0 x 10-3 M. These problems were resolved by modifying the buffers utilized during chromatography and increasing the dimensions of the affinity column, and a two-stage procedure consisting of cation-exchange chromatography followed by affinity chromatography was used to purify each of the four variants of staphylococcal β-lactamase. The mean specific activities of the purified type A, B, C, and D β-lactamases were 44.6, 12.2, 10.6, and 30.8 μmol of nitrocefin hydrolyzed per min/mg of protein, respectively. Dimer formation, presumably from intramolecular cysteine-cysteine cross-linking, was observed with the type D β-lactamase but not with the type A, B, or C enzyme.