title: Deciphering the roles of BamB and its interaction with BamA in outer membrane biogenesis, T3SS expression and virulence in Salmonella.
abstract: The folding and insertion of β-barrel proteins in the outer membrane of Gram-negative bacteria is mediated by the BAM complex, which is composed of the outer membrane protein BamA and four lipoproteins BamB to BamE. In Escherichia coli and/or Salmonella, the BamB lipoprotein is involved in (i) β-barrel protein assembly in the outer membrane, (ii) outer membrane permeability to antibiotics, (iii) the control of the expression of T3SS which are major virulence factors and (iv) the virulence of Salmonella. In E. coli, this protein has been shown to interact directly with BamA. In this study, we investigated the structure-function relationship of BamB in order to assess whether the roles of BamB in these phenotypes were inter-related and whether they require the interaction of BamB with BamA. For this purpose, recombinant plasmids harbouring point mutations in bamB were introduced in a ΔSalmonella bamB mutant. We demonstrated that the residues L173, L175 and R176 are crucial for all the roles of BamB and for the interaction of BamB with BamA. Moreover, the results obtained with a D229A BamB variant, which is unable to immunoprecipitate BamA, suggest that the interaction of BamB with BamA is not absolutely necessary for BamB function in outer-membrane protein assembly, T3SS expression and virulence. Finally, we showed that the virulence defect of the ΔbamB mutant is not related to its increased susceptibility to antimicrobials, as the D227A BamB variant fully restored the virulence of the mutant while having a similar antibiotic susceptibility to the ΔbamB strain. Overall, this study demonstrates that the different roles of BamB are not all inter-related and that L173, L175 and R176 amino-acids are privileged sites for the design of BamB inhibitors that could be used as alternative therapeutics to antibiotics, at least against Salmonella.
authors.affiliation: INRA, UMR1282 Infectiologie et Santé Publique, Nouzilly, France.
authors.forename: Fatémeh
authors.initials: F
authors.lastname: Namdari
authors.forename: Genaro Alejandro
authors.initials: GA
authors.lastname: Hurtado-Escobar
authors.forename: Nadia
authors.initials: N
authors.lastname: Abed
authors.forename: Jérôme
authors.initials: J
authors.lastname: Trotereau
authors.forename: Yann
authors.initials: Y
authors.lastname: Fardini
authors.forename: Etienne
authors.initials: E
authors.lastname: Giraud
authors.forename: Philippe
authors.initials: P
authors.lastname: Velge
authors.forename: Isabelle
authors.initials: I
authors.lastname: Virlogeux-Payant
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D051379:Mice; D008807:Mice, Inbred BALB C; D017354:Point Mutation; D025941:Protein Interaction Mapping; D012475:Salmonella / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D012481:Salmonella Infections, Animal / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism / Q000635:transmission*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D037521:Virulence Factors