LytA

LytA is the major autolysin of Streptococcus pneumoniae, encoded by the lytA gene. It is a surface-associated enzyme that mediates autolysis by cleaving the peptidoglycan layer of the bacterial cell wall. The enzyme is organized with an N-terminal catalytic domain and a C-terminal choline-binding domain that binds to phosphorylcholine residues in teichoic acids, anchoring the protein to the cell wall and targeting it to its substrate.

The catalytic activity of LytA is broadly described as an N-acetylmuramoyl-L-alanine amidase, which cleaves the amide bond within the peptidoglycan backbone. This enzymatic action weakens the cell wall, and when activated, leads to cell lysis and the release of intracellular contents. LytA activity is tightly regulated and typically associated with specific growth phases and environmental cues. It is more active during late exponential or stationary phase and can be stimulated by cellular stress or antibiotics that perturb cell wall synthesis, such as beta-lactams, which promote autolysis.

Biological and clinical significance of LytA includes its contribution to virulence and biofilm dynamics through the release of pneumolysin and other cytoplasmic components following autolysis. The enzyme also influences horizontal gene transfer and DNA release in pneumococcal populations. LytA serves as a model for studying bacterial autolysis and its role in pathogenesis and host–pathogen interactions.

See also: autolysin, Streptococcus pneumoniae.