Non‐Hydrolytic β‐Lactam Antibiotic Fragmentation by l, d‐Transpeptidases and Serine β‐Lactamase Cysteine Variants. (21st January 2019) - Lohans, Christopher T.
Abstract: Enzymes often use nucleophilic serine, threonine, and cysteine residues to achieve the same type of reaction; the underlying reasons for this are not understood. While bacteriald, d ‐transpeptidases (penicillin‐binding proteins) employ a nucleophilic serine, l, d ‐transpeptidases use a nucleophilic cysteine. The covalent complexes formed byl, d ‐transpeptidases with some β‐lactam antibiotics undergo non‐hydrolytic fragmentation. This is not usually observed for penicillin‐binding proteins, or for the related serine β‐lactamases. Replacement of the nucleophilic serine of serine β‐lactamases with cysteine yields enzymes which fragment β‐lactams via a similar mechanism as thel, d ‐transpeptidases, implying the different reaction outcomes are principally due to the formation of thioester versus ester intermediates. The results highlight fundamental differences in the reactivity of nucleophilic serine and cysteine enzymes, and imply new possibilities for the inhibition of nucleophilic enzymes.