BAM is a conserved molecular machine, the central component of which is BamA. Orthologues of BamA are found in all Gram-negative bacteria, chloroplasts and mitochondria where it is required for the folding and insertion of β-barrel containing integral outer membrane proteins (OMPs) into the outer membrane. BamA binds unfolded β-barrel precursors via the five polypeptide transport-associated (POTRA) domains at its N-terminus. The C-terminus of BamA folds into a β-barrel domain, which tethers BamA to the outer membrane and is involved in OMP insertion. BamA orthologues are found in all Gram-negative bacteria and appear to function in a species-specific manner. Here we investigate the nature of this species-specificity by examining whether chimeric Escherichia coli BamA fusion proteins, carrying either the β-barrel or POTRA domains from various BamA orthologues, can functionally replace E. coli BamA. We demonstrate that the β-barrel domains of many BamA orthologues are functionally interchangeable. We show that defects in the orthologous POTRA domains can be rescued by compensatory mutations within the β-barrel. These data reveal that the POTRA and barrel domains must be precisely aligned to ensure efficient OMP insertion.
Bibliographical note© 2015 The Authors. Molecular Microbiology published by John Wiley & Sons Ltd.
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Funding: Medical Research Council
- Bacterial Outer Membrane Proteins/chemistry
- Escherichia coli/genetics
- Escherichia coli Proteins/chemistry
- Gram-Negative Bacteria/genetics
- Models, Molecular
- Molecular Sequence Data
- Protein Conformation
- Protein Folding
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Recombinant Fusion Proteins/genetics
- Species Specificity