The G132S Mutation Enhances the Resistance of Mycobacterium tuberculosis β-Lactamase against Sulbactam

The current rise of antibiotic resistant forms of Mycobacterium tuberculosis is a global health threat that calls for new antibiotics. The beta-lactamase BlaC of this pathogen prevents the use of beta-lactam antibiotics, except in combination with a beta-lactamase inhibitor. To understand if exposure to such inhibitors can easily result in resistance, a BlaC evolution experiment was performed, studying the evolutionary adaptability against the inhibitor sulbactam. Several amino acid substitutions in BlaC were shown to confer reduced sensitivity to sulbactam. The G132S mutation causes a reduction in the rate of nitrocefin and ampicillin hydrolysis and simultaneously reduces the sensitivity for sulbactam inhibition. Introduction of the side chain moiety of Ser132 causes the 104-105 peptide bond to assume the cis conformation and the side chain of Ser104 to be rotated toward the sulbactam adduct with which it forms a hydrogen bond not present in the wild-type enzyme. The gatekeeper residue Ile105 also moves. These changes in the entrance of the active site can explain the decreased affinity of G132S BlaC for both substrates and sulbactam. Our results show that BlaC can easily acquire a reduced sensitivity for sulbactam, with a single-amino acid mutation, which could hinder the use of combination therapies.

Automated summary

The rise of antibiotic resistant Mycobacterium tuberculosis poses a global health threat, necessitating the development of new antibiotics. A study on the evolution of BlaC showed that a single amino acid mutation can easily lead to reduced sensitivity to the inhibitor sulbactam, potentially hindering the use of combination therapies.