Computational and experimental analyses of alanine racemase suggest new avenues for developing allosteric small-molecule antibiotics

Abstract

Given the ever-present threat of antibacterial resistance, there is an urgent need to identify new antibacterial drugs and targets. One such target is alanine racemase (Alr), an enzyme required for bacterial cell-wall biosynthesis. Alr is an attractive drug target because it is essential for bacterial survival but is absent in humans. Here, we investigate the Alr from M. tuberculosis (MT), the pathogen responsible for human tuberculosis, as a model Alr enzyme. MT-Alr functions exclusively as an obligate homodimer formed by two identical monomers. Both monomers contribute to the overall composition of their active sites. Therefore, disrupting the dimer interface could inhibit MT-Alr activity. Using computational methods, we identified seven interfacial residues predicted to be responsible for MT-Alr dimerization. Mutating one of the seven residues, Lys261, to alanine resulted in a completely inactive enzyme. Further investigation suggested a potential drug-binding site near Lys261 that might be useful for allosteric drug discovery. SummaryThe bacterial protein alanine racemase (Alr) converts L-alanine to D-alanine, a critical component of the bacterial cell wall. Cycloserine, a known antibiotic, inhibits Alr by binding to the same pocket that alanine binds. Several human proteins have similar pockets, so cycloserine has severe side effects. We identified additional Alr pockets and discovered that altering one of them abolishes Alr activity. Molecules that bind this pocket may similarly impact Alr activity, helping to address the ongoing antibiotic resistance crisis.