{
  "abstract": "The Fc alpha-mu receptor (Fc/R) is an ancient Fc-receptor sharing common ancestry with the polymeric Ig receptor (pIgR) and binding polymeric IgM and IgA ligands. In several vertebrate lineages, including birds, Fc/R may serve as the sole IgM and IgA Fc receptor; yet its evolution and ligand-recognition mechanisms across vertebrates remain poorly understood. Here, we identify FCAMR expression in duck (Anas platyrhynchos, ap) lymphoid tissues and demonstrate that recombinantly expressed apFc/R ectodomain binds apIgM and apIgA ligands. apFc/R affinity was ~10-fold higher for apIgM versus apIgA and ~10-fold higher than mouse (mm) Fc/R. Cryo-EM structures of apFc/R in complex with pentameric apIgM (3.27 [A]) and tetrameric apIgA (3.57 [A]) showed three Ig-like domains (D1-D3) bound asymmetrically with 1:1 stoichiometry. Comparisons to avian pIgR, which contains four Ig-like domains (D1-D4), revealed overlapping contacts between apFc/R-D1 and pIgR-D1. apFc/R D2-D3 engaged sites similar to pIgR D3-D4, yet formed distinct contact networks. Parallel analysis of a mmFc/R-mmIgM structure (4.13 [A]) revealed mmFc/R's single Ig-domain bound analogous to apFc/R-D1 and to mammalian pIgR-D1, whereas downstream ectodomain regions were not observed. Collectively, the data elucidate PIGR-family mechanisms across vertebrates, providing a foundation for delineating common and divergent functions.",
  "abstract_shown": true,
  "affiliations": [
    "University of Illinois Urbana-Champaign"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "name": "M. Seal"
    },
    {
      "name": "W. N. Harrington"
    },
    {
      "name": "E. M. Flaugher"
    },
    {
      "name": "R. J. Webby"
    },
    {
      "affs": [
        0
      ],
      "name": "B. M. Stadtmueller"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3gm5w0f2zzx8h.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.11.06.764962",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.11.06.764962v1.full",
  "id": "3gm5w0f2zzx8h",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.11.06.764962v1",
  "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",
      "immunology"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.11.06.764962v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-06",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3gm5w0f2zzx8h.ris",
  "sources": [
    {
      "first_seen": "2026-11-10T00:27:11Z",
      "native_id": "10.64898/2026.11.06.764962",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.11.06.764962v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:immunology",
      "subfield": "immunology"
    }
  ],
  "title": "Structural evolution of Fcα/μR-mediated antibody recognition",
  "title_text": "Structural evolution of Fcα/μR-mediated antibody recognition",
  "type": "preprint",
  "updated_at": "2026-11-10T00:27:11Z",
  "url": "https://research.draconitic.com/paper/3gm5w0f2zzx8h",
  "venue": "bioRxiv",
  "versions": []
}