autolysins

Autolysins are endogenous peptidoglycan hydrolases produced by bacteria that mediate controlled remodeling and turnover of the cell wall. They participate in cell growth, division, and separation by cleaving specific bonds within the peptidoglycan sacculus, allowing insertion of new wall material and release of daughter cells.

Autolysins comprise several enzymatic families, including N-acetylmuramoyl-L-alanine amidases that cut the amide bond between MurNAc and L-alanine, endopeptidases that cleave peptide cross-links, glycosidases that hydrolyze glycosidic linkages, and lytic transglycosylases that cleave the glycan backbone with products different from simple hydrolysis. They can be secreted or wall-anchored and often act at the septum during division or at sites of wall turnover. Activity is tightly regulated to prevent destructive autolysis; regulators include inhibitors, environmental cues, and the balance with wall-synthetic enzymes.

Biological roles include separation of daughter cells after division, remodeling during growth and morphogenesis, turnover of old wall material, and, in some pathogens, contribution to virulence and biofilm dynamics. External stresses or antibiotic action can trigger autolysis, either as a defensive mechanism or as a collateral effect, aiding cell lysis and release of intracellular contents. Beta-lactam antibiotics, for example, can induce autolysin-mediated lysis by weakening the wall and enabling enzymatic attack.

Examples include AmiA/B/C amidases in gram-negative rods, LytA in Streptococcus pneumoniae, and Atl family autolysins in Staphylococcus aureus and related species.