Enterococcus NlpC/p60 Peptidoglycan Hydrolase SagA Localizes to Sites of Cell Division and Requires Only a Catalytic Dyad for Protease Activity.

Peptidoglycan is a vital component of the bacterial cell wall, and its dynamic remodeling by NlpC/p60 hydrolases is crucial for proper cell division and survival. Beyond these essential functions, we previously discovered that Enterococcus species express and secrete the NlpC/p60 hydrolase-secreted antigen A (SagA), whose catalytic activity can modulate host immune responses in animal models. However, the localization and peptidoglycan hydrolase activity of SagA in Enterococcus was still unclear. In this study, we show that SagA contributes to a triseptal structure in dividing cells of enterococci and localizes to sites of cell division through its N-terminal coiled-coil domain. Using molecular modeling and site-directed mutagenesis, we identify amino acid residues within the SagA-NlpC/p60 domain that are crucial for catalytic activity and potential substrate binding. Notably, these studies revealed that SagA may function via a catalytic Cys-His dyad instead of the predicted Cys-His-His triad, which is conserved in SagA orthologs from other Enterococcus species. Our results provide key additional insight into peptidoglycan remodeling in Enterococcus by SagA NlpC/p60 hydrolases.