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PreprintCited by 10Bacterial Genetics and BiotechnologyAdvanced Electron Microscopy Techniques and ApplicationsLipid Membrane Structure and Behavior

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Discovery of a distinct BAM complex in the Bacteroidetes

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Silale, Augustinas, Madej, Mariusz, Mikruta, Katarzyna, Frey, Andrew M., Hart, Adam J., Baslé, Arnaud, Scavenius, Carsten, Enghild, Jan J., Trost, Matthias, Hirt, Robert P., van den Berg, Bert·2025·Nature Microbiology
DOI 10.1101/2025.01.31.636011PMC PMC12578637

Preprint — published as 10.1038/s41564-025-02132-2

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Abstract

The BAM (β-barrel assembly machinery) complex is an evolutionarily conserved, multiprotein machine that catalyses the folding and membrane insertion of newly synthesised β-barrel outer membrane (OM) proteins in Gram-negative bacteria. Based on Proteobacteria, bacterial BAM is also structurally conserved, with an essential BamAD core and up to three auxiliary periplasmic lipoproteins of poorly defined function. Here we show, using structural biology, quantitative proteomics and functional assays, that the BAM complex is radically different within the Bacteroidetes, a large and important phylum widely distributed within the environment and animal microbiomes. Cryogenic electron microscopy (cryo-EM) structures of BAM complexes from the human gut symbiont Bacteroides thetaiotaomicron and the human oral pathogen Porphyromonas gingivalis show similar, seven-component complexes of ∼325 kDa in size with most of the mass in the extracellular space. In addition to canonical BamA and BamD, the complexes contain an integral OM protein named BamF that is essential and intimately associated with BamA, as well as four surface-exposed lipoproteins (SLPs) named BamG-J. Together, BamF-J form a large, extracellular dome that likely serves as an assembly cage for the β-barrel-SLP complexes that are a hallmark of the Bacteroidetes. Our data suggest that BAM functionality in Bacteroidetes is substantially expanded from that in Proteobacteria and underscores the importance of studying other phyla for a more complete understanding of fundamental biological processes.

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Metadata

Authors
Silale, A., Madej, M., Mikruta, K., Frey, A. M., Hart, A. J., Baslé, A., Scavenius, C., Enghild, J. J., Trost, M., Hirt, R. P., & van den Berg, B.
Affiliations
  • Newcastle University (GB)
  • Jagiellonian University (PL)
  • Aarhus University (DK)
Corresponding author
  • Madej, Mariusz
  • van den Berg, Bert
ORCID
Venue
Nature Microbiology
Publisher
openRxiv
Published
2025-02-01
Volume
10
Issue
11
Pages
2845-2859
ISSN
2058-5276 (ISSN-L)
DOI
10.1101/2025.01.31.636011
PMC
PMC12578637
OpenAlex
W4414690685
Cited by
10
References
2
Citations by year
2026: 6 · 2025: 4
FWCI
5.88
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature Microbiology (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Research Explorer (The University of Manchester) (publishedVersion)
  • Jagiellonian University Repository (Jagiellonian University) (submittedVersion, cc-by-nc-nd)
  • Scopus (Elsevier) (submittedVersion, cc-by)
  • Newcastle University ePrints (Newcastle Univesity) (cc-by)
Funders
Wellcome Trust (214222/Z/18/Z, 221524/Z/20/Z, 108466/Z/15/Z)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Bacterial Genetics and Biotechnology
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Structural Biology › Advanced Electron Microscopy Techniques and Applications
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Lipid Membrane Structure and Behavior
Keywords
β-barrel assembly machinery, BAM complex, Bacteroidetes, Bacteroides thetaiotaomicron, Porphyromonas gingivalis, BamA, β-barrel outer membrane proteins, protein folding, membrane insertion, lipoprotein assembly, Gram-negative bacteria
MeSH terms
Bacteroides thetaiotaomicron, Bacterial Outer Membrane Proteins, Humans, Lipoproteins, Models, Molecular, Porphyromonas gingivalis, Protein Folding, Cryoelectron Microscopy, Proteomics

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