title: Binding of the immunity protein inactivates colicin M.
abstract: Colicin M (Cma) displays a unique mode of action in that it inhibits peptidoglycan and lipopolysaccharide biosynthesis through interference with bactoprenyl phosphate recycling. Protection of Cma-producing cells by the immunity protein (Cmi) was studied. The amount of Cmi determined the degree of inhibition of in vitro peptidoglycan synthesis by Cma. In cells, immunity breakdown could be achieved by overexpression of the Cma uptake system. Full immunity was restored after raising the cmi gene copy number. In sphaeroplasts, Cmi was degraded by trypsin, but this could be prevented by the addition of Cma. The N-terminal end includes the only hydrophobic amino acid sequence of Cmi, suggesting a function in anchoring of Cmi in the cytoplasmic membrane. It is proposed that Cmi does not act catalytically but binds Cma at the periplasmic face of the cytoplasmic membrane, thereby resulting in Cma inactivation. Two other possible modes of colicin M immunity, interference of Cmi with the uptake of Cma, and interaction of Cmi with the target of Cma, were ruled out by the data.
authors.affiliation: Mikrobiologie II, Auf der Morgenstelle 28, Universität, Tübingen, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Olschläger
authors.forename: A
authors.initials: A
authors.lastname: Turba
authors.forename: V
authors.initials: V
authors.lastname: Braun
mesh_terms: D000595:Amino Acid Sequence; D001414:Bacitracin / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003087:Colicins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010457:Peptidoglycan / Q000096:biosynthesis*; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000187:drug effects / Q000378:metabolism; D011991:Receptors, Virus; D013104:Spheroplasts / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D010457:Peptidoglycan; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011991:Receptors, Virus; C488856:cmI protein, E coli; C007104:colicin immunity proteins; C028593:colicin receptor, E coli; D001414:Bacitracin; D014357:Trypsin