title: Cofactor bypass variants reveal a conformational control mechanism governing cell wall polymerase activity.
abstract: To fortify their cytoplasmic membrane and protect it from osmotic rupture, most bacteria surround themselves with a peptidoglycan (PG) exoskeleton synthesized by the penicillin-binding proteins (PBPs). As their name implies, these proteins are the targets of penicillin and related antibiotics. We and others have shown that the PG synthases PBP1b and PBP1a of Escherichia coli require the outer membrane lipoproteins LpoA and LpoB, respectively, for their in vivo function. Although it has been demonstrated that LpoB activates the PG polymerization activity of PBP1b in vitro, the mechanism of activation and its physiological relevance have remained unclear. We therefore selected for variants of PBP1b (PBP1b*) that bypass the LpoB requirement for in vivo function, reasoning that they would shed light on LpoB function and its activation mechanism. Several of these PBP1b variants were isolated and displayed elevated polymerization activity in vitro, indicating that the activation of glycan polymer growth is indeed one of the relevant functions of LpoB in vivo. Moreover, the location of amino acid substitutions causing the bypass phenotype on the PBP1b structure support a model in which polymerization activation proceeds via the induction of a conformational change in PBP1b initiated by LpoB binding to its UB2H domain, followed by its transmission to the glycosyl transferase active site. Finally, phenotypic analysis of strains carrying a PBP1b* variant revealed that the PBP1b-LpoB complex is most likely not providing an important physical link between the inner and outer membranes at the division site, as has been previously proposed.
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115;
authors.forename: Monica
authors.initials: M
authors.lastname: Markovski
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115;
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Bohrhunter
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Tania J
authors.initials: TJ
authors.lastname: Lupoli
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115;
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Uehara
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Suzanne
authors.initials: S
authors.lastname: Walker
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Kahne
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115; thomas_bernhardt@hms.harvard.edu.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Bernhardt
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D001665:Binding Sites; D002473:Cell Wall / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D003067:Coenzymes / Q000737:chemistry / Q000648:ultrastructure; D003198:Computer Simulation; D004789:Enzyme Activation; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D046915:Penicillin-Binding Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D001425:Bacterial Outer Membrane Proteins; D003067:Coenzymes; D029968:Escherichia coli Proteins; C000592364:LpoB protein, E coli; D046915:Penicillin-Binding Proteins
keywords: PBP; cell wall; murein; penicillin; peptidoglycan