Dynamic association of BAM complex modules includes surface exposure of the lipoprotein BamC.
The β-barrel assembly machinery (BAM) complex drives the assembly of β-barrel proteins into the outer membrane of gram-negative bacteria. It is composed of five subunits: BamA, BamB, BamC, BamD, and BamE. We find that the BAM complex isolated from the outer membrane of Escherichia coli consists of a core complex of BamA:B:C:D:E and, in addition, a BamA:B module and a BamC:D module. In the absence of BamC, these modules are destabilized, resulting in increased protease susceptibility of BamD and BamB. While the N-terminus of BamC carries a highly conserved region crucial for stable interaction with BamD, immunofluorescence, immunoprecipitation, and protease-sensitivity assays show that the C-terminal domain of BamC, composed of two helix-grip motifs, is exposed on the surface of E. coli. This unexpected topology of a bacterial lipoprotein is reminiscent of the analogous protein subunits from the mitochondrial β-barrel insertion machinery, the SAM complex. The modular arrangement and topological features provide new insight into the architecture of the BAM complex, towards a better understanding of the mechanism driving β-barrel membrane protein assembly.
Department of Biochemistry and Molecular Biology, Monash University, Melbourne 3800, Australia.
Chaille T
CT
Webb
Joel
J
Selkrig
Andrew J
AJ
Perry
Nicholas
N
Noinaj
Susan K
SK
Buchanan
Trevor
T
Lithgow
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D058635:Lipid-Linked Proteins / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary
D001425:Bacterial Outer Membrane Proteins; C556681:BamC protein, E coli; C513739:BamD protein, E coli; D029968:Escherichia coli Proteins; D058635:Lipid-Linked Proteins; D008074:Lipoproteins