LytM family endopeptidase LmdC is controlled by regulated auto processing and proteolytic destruction in Pseudomonas aeruginosa

ABSTRACT Enzymes that cleave the bacterial peptidoglycan sacculus, known collectively as autolysins, are critical for growth, division and morphogenesis, but their activities must be carefully controlled to avoid catastrophic lysis. Some autolysin control mechanisms have emerged, but we still know little about how most of them are regulated. Here, we report a novel control mechanism for the LytM/M23 family endopeptidase PA4404 in P. aeruginosa , which we have named LmdC. We have discovered that LmdC is auto catalytically cleaved into N- and C-terminal domains that are then degraded by the carboxyl-terminal processing proteases Prc and CtpA respectively. The effects of various mutations on LmdC-linked β-lactam resistance suggested that full length LmdC is the functional enzyme, with its auto catalytic cleavage serving only to initiate its proteolytic destruction. The auto catalytic cleavage of LmdC was inhibited by overproducing a polymer-forming cytoskeletal protein bactofilin homolog encoded by PA0664, which we named Baf, and a protein of unknown function encoded by PA0663, which we named Api ( a uto p rocessing inhibitor). We hypothesize that Baf and Api could promote a location specific role for LmdC. In this scenario, the dangerous potential for any free LmdC to cleave peptidoglycan at the wrong place would be prevented by its immediate auto processing and degradation. The widespread co-occurrence and linkage of lmdC and baf homologs, coupled with conserved features of those LmdC homologs, makes it likely that regulated LmdC auto processing is a widely conserved control mechanism. IMPORTANCE A peptidoglycan cell wall is an essential component of almost all bacterial cells and antibiotics that interfere with its synthesis have been critical infection treatments for decades. Peptidoglycan must also be cleaved to allow incorporation of new material for growth and division. However, the autolysin enzymes that cleave peptidoglycan must be controlled to prevent cell rupture. It is not known how this control is achieved in most cases, but it is an important area of research because these control mechanisms could be targets for therapeutic intervention. This study describes the discovery of regulated auto catalytic processing as an autolysin control mechanism in the human pathogen Pseudomonas aeruginosa , which is also likely to be widely conserved in other species.