{
  "abstract": "Many photosynthetic bacteria rely on the nitrogenase-like dark-operative protochlorophyllide oxidoreductase (DPOR) to sustain (bacterio)chlorophyll synthesis in the dark. DPOR couples ATP hydrolysis to electron transfer from a reducing component (L-protein) to a catalytic component (NB-protein) that reduces protochlorophyllide. NB-protein is an 2{beta}2 heterotetramer, and each heterodimeric half contains an active site and a [Fe4S4] cluster. Although the two halves are identical, they react sequentially rather than in parallel. How the two halves communicate has remained unknown. Here we show, using Cu K-edge x-ray absorption spectroscopy and cryo-EM, that the NB-protein tetramer interface holds a binuclear, sulfur-bridged [Cu2S2] cluster. Each Cu is reduced and three-coordinate, with short Cu-S and Cu-Cu distances (2.26 and 2.62 &Aring). Mutagenesis excludes the nearest cysteine as the bridging ligand, supporting inorganic sulfide as the most likely sulfur donor. To our knowledge, this is the first sulfide-bridged dicopper cluster identified in a protein. The cluster is conserved in three purple non-sulfur bacteria and connects the BchB C-terminal helices that contact opposing active sites. Loss of Cu abolishes DPOR activity and asymmetric L-protein binding without disturbing overall fold. We propose that the cluster relays substrate-binding information between active sites, suggesting a metal-mediated mechanism for cooperativity in nitrogenase-like enzymes.",
  "abstract_shown": true,
  "affiliations": [
    "SLAC National Accelerator Laboratory"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "name": "K. Zhao"
    },
    {
      "name": "R. Kashyap"
    },
    {
      "name": "M. J. Abernathy"
    },
    {
      "name": "E. Antony"
    },
    {
      "affs": [
        0
      ],
      "name": "R. Sarangi"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fwec5s621pqc5.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.11.03.763803",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.11.03.763803v1.full",
  "id": "fwec5s621pqc5",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.11.03.763803v1",
  "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",
      "biochemistry"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.11.03.763803v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fwec5s621pqc5.ris",
  "sources": [
    {
      "first_seen": "2026-11-06T00:22:14Z",
      "native_id": "10.64898/2026.11.03.763803",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.11.03.763803v1"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "biorxiv:biochemistry",
      "subfield": "general"
    }
  ],
  "title": "A Binuclear Cluster Supports Functional Asymmetry in Dark-Operative Protochlorophyllide Reductase",
  "title_text": "A Binuclear Cluster Supports Functional Asymmetry in Dark-Operative Protochlorophyllide Reductase",
  "type": "preprint",
  "updated_at": "2026-11-07T00:20:59Z",
  "url": "https://research.draconitic.com/paper/fwec5s621pqc5",
  "venue": "bioRxiv",
  "versions": []
}