Formation of a β-barrel membrane protein is catalyzed by the interior surface of the assembly machine protein BamA

• Published in: eLife Vol. 8
• Main Authors: Lee, James, Tomasek, David, Santos, Thiago Ma, May, Mary D, Meuskens, Ina, Kahne, Daniel
• Format: Journal Article
• Language: English
• Published: England eLife Sciences Publications Ltd 14-11-2019; eLife Sciences Publications, Ltd
• Subjects: Amino Acid Motifs; Amino acids; Bacteria; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Bam complex; beta barrel; Binding Sites; Biochemistry and Chemical Biology; Cell Membrane; Chloroplasts; Cloning, Molecular; Crystallography, X-Ray; E coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli - ultrastructure; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Gene Expression; Genetic Vectors - chemistry; Genetic Vectors - metabolism; Gram-negative bacteria; membrane protein folding; Membrane proteins; Membranes; Microbiology and Infectious Disease; Mitochondria; Models, Molecular; Molecular modelling; Mutation; outer membrane; Protein Binding; Protein Conformation, beta-Strand; Protein Folding; Protein Interaction Domains and Motifs; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Substrate Specificity; outer membrane; gram-negative bacteria; Bam complex; chemical biology; infectious disease; biochemistry; microbiology; E. coli; beta barrel; membrane protein folding
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.49787

The β-barrel assembly machine (Bam) complex in Gram-negative bacteria and its counterparts in mitochondria and chloroplasts fold and insert outer membrane β-barrel proteins. BamA, an essential component of the complex, is itself a β-barrel and is proposed to play a central role in assembling other barrel substrates. Here, we map the path of substrate insertion by the Bam complex using site-specific crosslinking to understand the molecular mechanisms that control β-barrel folding and release. We find that the C-terminal strand of the substrate is stably held by BamA and that the N-terminal strands of the substrate are assembled inside the BamA β-barrel. Importantly, we identify contacts between the assembling β-sheet and the BamA interior surface that determine the rate of substrate folding. Our results support a model in which the interior wall of BamA acts as a chaperone to catalyze β-barrel assembly.