title: Activation of the Escherichia coli β-barrel assembly machine (Bam) is required for essential components to interact properly with substrate.
abstract: The outer membrane (OM) of gram-negative bacteria such as Escherichia coli contains lipoproteins and integral β-barrel proteins (outer-membrane proteins, OMPs) assembled into an asymmetrical lipid bilayer. Insertion of β-barrel proteins into the OM is mediated by a protein complex that contains the OMP BamA and four associated lipoproteins (BamBCDE). The mechanism by which the Bam complex catalyzes the assembly of OMPs is not known. We report here the isolation and characterization of a temperature-sensitive lethal mutation, bamAE373K, which alters the fifth polypeptide transport-associated domain and disrupts the interaction between the BamAB and BamCDE subcomplexes. Suppressor mutations that map to codon 197 in bamD restore Bam complex function to wild-type levels. However, these suppressors do not restore the interaction between BamA and BamD; rather, they bypass the requirement for stable holocomplex formation by activating BamD. These results imply that BamA and BamD interact directly with OMP substrates.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
authors.forename: Dante P
authors.initials: DP
authors.lastname: Ricci
authors.forename: Christine L
authors.initials: CL
authors.lastname: Hagan
authors.forename: Daniel
authors.initials: D
authors.lastname: Kahne
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Silhavy
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology*; D003062:Codon / Q000235:genetics; D017124:Conserved Sequence; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D008051:Lipid Bilayers; D058635:Lipid-Linked Proteins / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D020125:Mutation, Missense; D017354:Point Mutation; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; C557407:BamB protein, E coli; C556681:BamC protein, E coli; C513739:BamD protein, E coli; C523551:BamE protein, E coli; D003062:Codon; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D058635:Lipid-Linked Proteins; D046912:Multiprotein Complexes