Conserved mechanism of cell-wall synthase regulation revealed by the identification of a new PBP activator in .

Penicillin-binding proteins (PBPs) are synthases required to build the essential peptidoglycan (PG) cell wall surrounding most bacterial cells. The mechanisms regulating the activity of these enzymes to control PG synthesis remain surprisingly poorly defined given their status as key antibiotic targets. Several years ago, the outer-membrane lipoprotein LpoB was identified as a critical activator of PBP1b (PBP1b), one of the major PG synthases of this organism. Activation of PBP1b is mediated through the association of LpoB with a regulatory domain on PBP1b called UB2H. Notably, also encodes PBP1b (PBP1b), which possesses a UB2H domain, but this bacterium lacks an identifiable LpoB homolog. We therefore searched for potential PBP1b activators and identified a lipoprotein unrelated to LpoB that is required for the in vivo activity of PBP1b. We named this protein LpoP and found that it interacts directly with PBP1b in vitro and is conserved in many Gram-negative species. Importantly, we also demonstrated that LpoP-PBP1b as well as an equivalent protein pair from can fully substitute for LpoB-PBP1b in for PG synthesis. Furthermore, we show that amino acid changes in PBP1b that bypass the LpoP requirement map to similar locations in the protein as changes promoting LpoB bypass in PBP1b. Overall, our results indicate that, although different Gram-negative bacteria activate their PBP1b synthases with distinct lipoproteins, they stimulate the activity of these important drug targets using a conserved mechanism.