{
  "abstract": "Bacteroides are abundant gut bacteria with diverse polysaccharide metabolizing capabilities encoded by co-transcribed polysaccharide utilization loci (PULs). The starch utilization system (Sus) is required for starch and a-glucan metabolism in Bacteroides thetaiotaomicron and has served as a model for PUL studies. However, the mechanism of maltooligosaccharide (MOS) transport and the architecture of the SusCD complex remain incompletely understood. Here, we used cryo-electron microscopy to capture multiple transport-relevant conformations of the SusD lipoprotein and the TonB-dependent transporter SusC in both unliganded and ligand-bound states. In the absence of ligand, SusCD adopts three conformations including an open state in which SusD is displaced from SusC, a state containing the SusC plug, and a state lacking density for the SusC plug. Three-dimensional variability analysis of the structure where SusD is displaced from SusC reveals continuous SusD mobility coupled to movement of the SusC N-terminus. The maltoheptaose-bound SusCD structure reveals two binding sites, one at the SusD-SusC interface and a second within SusC, indicating how MOS stabilizes a closed SusCD assembly. Notably, all structures show that SusCD is a heterodimer, unlike other Sus-like transporters that assemble into SusCD heterotetramers. Native mass spectrometry confirms this heterodimeric stoichiometry, and comparisons with other SusCD-like complexes suggest a structural basis for this distinct assembly of SusCD. Together, these data define substrate binding and intermediate transport states in a canonical PUL system and reveal architectural divergence among Sus-like carbohydrate transport complexes in Bacteroides.",
  "abstract_shown": true,
  "affiliations": [
    "University of Michigan Microbiology and Immunology"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "name": "M. C. Cadigan"
    },
    {
      "name": "N. Rivera-Fuentes"
    },
    {
      "name": "W. Salmen"
    },
    {
      "name": "J. R. Roberts"
    },
    {
      "name": "B. Ruotolo"
    },
    {
      "name": "M. D. Ohi"
    },
    {
      "affs": [
        0
      ],
      "name": "N. M. Koropatkin"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fcc4m1vkn9yt9.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.16.752182",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.09.16.752182v1.full",
  "id": "fcc4m1vkn9yt9",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.09.16.752182v1",
  "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",
      "microbiology"
    ],
    [
      "openalex",
      "2505|Enzyme Structure and Function"
    ]
  ],
  "openalex": "W7213620694",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.09.16.752182v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fcc4m1vkn9yt9.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:11Z",
      "native_id": "10.64898/2026.09.16.752182",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.09.16.752182v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:microbiology",
      "subfield": "microbiology"
    }
  ],
  "title": "Structural analyses of a heterodimeric SusCD complex captures intermediate states of maltooligosaccharide transport",
  "title_text": "Structural analyses of a heterodimeric SusCD complex captures intermediate states of maltooligosaccharide transport",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:11Z",
  "url": "https://research.draconitic.com/paper/fcc4m1vkn9yt9",
  "venue": "bioRxiv",
  "versions": []
}