Bacterial outer membrane proteins assemble via asymmetric interactions with the BamA β-barrel

• Published in: Nature communications Vol. 10; no. 1; pp. 3358 - 13
• Main Authors: Doyle, Matthew T, Bernstein, Harris D
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 26.07.2019; Nature Publishing Group UK; Nature Portfolio
• Subjects: Assembly; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Cell Membrane - chemistry; Cell Membrane - genetics; Cell Membrane - metabolism; Crosslinking; E coli; Escherichia coli - chemistry; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Integration; Lipids; Membrane proteins; Outer membrane proteins; Polypeptides; Protein Binding; Protein Domains; Proteins; Substrates
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-11230-9

The integration of β-barrel proteins into the bacterial outer membrane (OM) is catalysed by the β-barrel assembly machinery (BAM). The central BAM subunit (BamA) itself contains a β-barrel domain that is essential for OM protein biogenesis, but its mechanism of action is unknown. To elucidate its function, here we develop a method to trap a native Escherichia coli β-barrel protein bound stably to BamA at a late stage of assembly in vivo. Using disulfide-bond crosslinking, we find that the first β-strand of a laterally 'open' form of the BamA β-barrel forms a rigid interface with the C-terminal β-strand of the substrate. In contrast, the lipid-facing surface of the last two BamA β-strands forms weaker, conformationally heterogeneous interactions with the first β-strand of the substrate that likely represent intermediate assembly states. Based on our results, we propose that BamA promotes the membrane integration of partially folded β-barrels by a 'swing' mechanism.