{
  "abstract": "The {beta}-barrel assembly machinery (BAM) catalyzes the folding and insertion of {beta}-barrel outer membrane proteins (OMPs) in Gram-negative bacteria without an external energy source. BAM comprises the central subunit BamA and associated lipoproteins, with BamA forming a conformationally dynamic lateral gate. Although substrate-engaged structures have revealed key steps in OMP assembly, how substrate-free BamA closes its lateral gate and which conformations it adopts in a lipid bilayer remain unclear. Here, we determined cryo-EM structures of the Escherichia coli (E. coli) BAM complex in three detergents and in Saposin A nanodiscs composed of E. coli polar lipids. In addition to the canonical outward-open (OO) state, we identified an occluded (OC) state in which both the lateral gate and the periplasmic opening of the BamA barrel are closed. OC predominated in lipid-reconstituted BAM that retained OMP-folding activity, indicating that this state is substantially populated in a functional BAM ensemble within a lipid bilayer. We also identified a semi-occluded (sOC) state in which {beta}1-{beta}2 adopts an OC-like closed position while rearrangement of {beta}16 remains incomplete. Comparison of OO, sOC, and OC reveals asynchronous rearrangements of the {beta}1-{beta}2 and {beta}16 regions, with {beta}1-{beta}2 movement occurring without complete repositioning of {beta}16. Re-examination of previously reported lipid-embedded BAM structures further highlights the importance of local map quality at the gate region for conformational assignment. Together, our findings expand the BamA conformational landscape beyond the conventional OO-inward-open (IO) framework to include OC and sOC as distinct structural states associated with lateral-gate closure following OMP insertion.",
  "abstract_shown": true,
  "affiliations": [
    "Division of Structural Medicine and Anatomy, Graduate School of Medicine, Kobe University, Hyogo, Japan; Department of Cell Biology, Graduate School of Medicine"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 6,
  "authors": [
    {
      "name": "T. Kato"
    },
    {
      "name": "H. Shigematsu"
    },
    {
      "name": "K. Takeuchi"
    },
    {
      "name": "M. Suzuki"
    },
    {
      "name": "R. Nitta"
    },
    {
      "affs": [
        0
      ],
      "name": "T. Imasaki"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4k7p0yst5p1xp.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.10.20.760484",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.10.20.760484v1.full",
  "id": "4k7p0yst5p1xp",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.10.20.760484v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "molecular biology"
    ],
    [
      "openalex",
      "1315|Advanced Electron Microscopy Techniques and Applications"
    ]
  ],
  "openalex": "W7223094649",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.10.20.760484v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-20",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4k7p0yst5p1xp.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:28:57Z",
      "native_id": "10.64898/2026.10.20.760484",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.10.20.760484v1"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "biorxiv:molecular biology",
      "subfield": "molecular-biology"
    }
  ],
  "title": "CLOSING THE CONFORMATIONAL CYCLE OF THE BETA-BARREL ASSEMBLY MACHINERY",
  "title_text": "CLOSING THE CONFORMATIONAL CYCLE OF THE BETA-BARREL ASSEMBLY MACHINERY",
  "type": "preprint",
  "updated_at": "2026-10-30T12:28:57Z",
  "url": "https://research.draconitic.com/paper/4k7p0yst5p1xp",
  "venue": "bioRxiv",
  "versions": []
}