Reassessing the substrate specificities of the major Staphylococcus aureus peptidoglycan hydrolases lysostaphin and LytM

Orchestrated action of peptidoglycan (PG) synthetases and hydrolases is vital for bacterial growth and viability. Although the function of several PG synthetases e.g., penicillin binding proteins is well-understood, the function, regulation, and mechanism of action of the majority of PG hydrolases have remained elusive. Lysostaphin-like zinc-dependent metalloendopeptidases specifically hydrolyse the glycyl-glycine peptide bond in the notorious pathogen Staphylococcus aureus . In this work, we have employed NMR spectroscopy to study the substrate specificity of the well-established bactericide lysostaphin as well as pre-designated S. aureus autolysin LytM. Our results show that the substrate specificities of these highly homologous enzymes are divergent and formerly also inaccurately defined. Yet, we provide substrate-level evidence for the functional role of these enzymes. Indeed, we show that LytM and anti-staphylococcal bactericidin lysostaphin target the D-Ala-Gly cross-linked part of mature peptidoglycan. ### Competing Interest Statement The authors have declared no competing interest.