{
  "abstract": "The endonuclear symbiont Holospora obtusa invades the macronucleus of Paramecium caudatum using an infectious-form invasion-tip containing a major 89-kDa periplasmic protein implicated in escape from the host digestive vacuole and macronuclear invasion. Sequence-based analyses placed this protein within a Holospora-specific family and predicted an N-terminal membrane-anchoring module and a long alpha-helical C-terminal region. AlphaFold2 modeling followed by molecular dynamics indicated that the C-terminal region forms an antiparallel, spectrin-repeat-like helical solenoid containing a localized three-helix coiled-coil. The protein exhibits a large pH-dependent charge difference, becoming 55 units more positive at pH 4 than at pH 7. Independent simulations at these pH values differed mainly in the relative orientation of the N-terminal core and C-terminal rod, described by DynDom as an approximately 35 degrees rigid-body rotation about a hinge centered on Gly291. However, none of the nearby glutamates (Glu273, Glu275, and Glu302) formed a pH-dependent salt bridge, and no specific protonation-dependent interaction responsible for the conformational difference was identified. We nonetheless propose, as a testable hypothesis, that acidification of the digestive vacuole may promote this reorientation, thereby repositioning the N-terminal membrane-anchoring module at the bacterial surface as an early step toward escape from the vacuole.",
  "abstract_shown": true,
  "affiliations": [
    "Yamaguchi University"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "name": "Y. Takenaka"
    },
    {
      "name": "T. Murai"
    },
    {
      "name": "T. Nakatsu"
    },
    {
      "name": "Y. Shigeri"
    },
    {
      "affs": [
        0
      ],
      "name": "M. Fujishima"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/bn1gey9bpbt3g.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.10.08.757700",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.10.08.757700v1.full",
  "id": "bn1gey9bpbt3g",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.10.08.757700v1",
  "language": null,
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "microbiology"
    ],
    [
      "openalex",
      "1312|Protein Structure and Dynamics"
    ]
  ],
  "openalex": "W7221333793",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.10.08.757700v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-08",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/bn1gey9bpbt3g.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:26:59Z",
      "native_id": "10.64898/2026.10.08.757700",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.10.08.757700v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:microbiology",
      "subfield": "microbiology"
    }
  ],
  "title": "Predicted structure of the 89-kDa invasion-tip protein of Holospora obtusa, an endonuclear symbiont of Paramecium caudatum, suggests a pH-dependent conformational change",
  "title_text": "Predicted structure of the 89-kDa invasion-tip protein of Holospora obtusa, an endonuclear symbiont of Paramecium caudatum, suggests a pH-dependent conformational change",
  "type": "preprint",
  "updated_at": "2026-10-30T12:26:59Z",
  "url": "https://research.draconitic.com/paper/bn1gey9bpbt3g",
  "venue": "bioRxiv",
  "versions": []
}