4hdj

Publication Abstract from PubMed

The assembly of beta-barrel Outer Membrane Proteins (OMPs) in the outer membrane is essential for gram-negative bacteria. The process requires the beta-Barrel Assembly Machine (BAM), a multiprotein complex that, in E. coli, is composed of the OMP BamA and four lipoproteins BamB-E. Whereas BamA and BamD are essential, deletion of BamB, C or E produce membrane permeability defects. Here we present the high-resolution structure of BamB from Pseudomonas aeruginosa. This protein can complement the deletion of bamB in E. coli indicating that they are functionally equivalent. Conserved structural features include an eight-bladed beta-propeller fold stabilized by tryptophan docking motifs with a central pore about 8 A in diameter at the narrowest point. This pore distinguishes BamB from related beta-propellers, such as quinoprotein dehydrogenases. However, a double mutation designed to block this pore was fully functional indicating that the opening is not essential. Two loops protruding from the bottom of the propeller are conserved and mediate binding to BamA. Conversely, an additional loop only present in E. coli BamB is not required for function. A cluster of highly conserved residues in a groove between blades 6 and 7 is crucial for proper BamB folding or biogenesis. It has been proposed that BamB may bind nascent OMPs by beta-augmentation to its propeller outer strands, or recognize the aromatic residue signature at the C-terminus of OMPs. However, Isothermal Titration Calorimetry experiments and structural analysis do not support these proposals. The structural and mutagenesis analysis suggests that the main function of BamB is to bind and modulate BamA, rather than directly interact with nascent OMPs.

Crystal structure of BamB from Pseudomonas aeruginosa and functional evaluation of its conserved structural features.,Jansen KB, Baker SL, Sousa MC PLoS One. 2012;7(11):e49749. doi: 10.1371/journal.pone.0049749. Epub 2012 Nov 26. PMID:23189157^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.