{
  "abstract": "Cyanobacteriochromes (CBCRs) are bilin-binding photoreceptors that photoconvert between long-lived, thermally stable states; in the red/green subfamily, photoexcitation converts the red-absorbing Pr state to the green-absorbing Pg state with a large blue shift. Here we quantify this Pr-Pg separation using quantum-mechanical/molecular-mechanical geometry optimization and wave function-based excited-state calculations. Calculated spectra reproduce the Pr-Pg trend and show that the shift is dominated by a Pg-specific increase in phycocyanobilin A-B inter-ring torsion, which truncates π-conjugation and widens the HOMO-LUMO gap. Protein electrostatics red-shifts both states similarly and thus does not set the Pr-Pg gap. Residue-chromophore interaction energies reveal state-dependent rewiring: Trp655 dominates in Pr and regulates the C-D dihedral orientation, whereas in Pg this role shifts to Ile691, and Thr658 becomes a major Pg-specific stabilizer acting at the A-B linkage. These results establish trapped-twist tuning as a geometry-driven mechanism with residue-level handles for engineering CBCR absorption.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya464-8601, Japan.",
    "Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furocho, Chikusa, Nagoya464-8601, Japan.",
    "Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo192-0397, Japan."
  ],
  "article_type": "research article",
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Shun Kohase"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Kazuhiro J Fujimoto",
      "orcid": "0000-0003-0286-3646"
    },
    {
      "affs": [
        2
      ],
      "name": "Rei Narikawa"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Takeshi Yanai",
      "orcid": "0000-0003-3933-8546"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6zd9b7h6b3crf.bib",
  "cited_by": 0,
  "doi": "10.1021/acs.jpcb.6c05208",
  "fulltext_url": "https://europepmc.org/articles/PMC13656734",
  "id": "6zd9b7h6b3crf",
  "issns": [
    "1520-6106",
    "1520-5207"
  ],
  "landing_url": "https://europepmc.org/article/MED/42916730",
  "language": "eng",
  "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": [
    [
      "openalex",
      "2804|Photoreceptor and optogenetics research"
    ]
  ],
  "openalex": "W7214704933",
  "pdf_url": "https://europepmc.org/articles/PMC13656734?pdf=render",
  "pmcid": "PMC13656734",
  "pmid": "42916730",
  "published": "2026-10-01",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6zd9b7h6b3crf.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:36Z",
      "native_id": "MED:42916730",
      "source": "europepmc",
      "url": "https://europepmc.org/article/MED/42916730"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "openalex:2804|Photoreceptor and optogenetics research",
      "subfield": "neuroscience"
    }
  ],
  "title": "A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes.",
  "title_text": "A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes.",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:20:36Z",
  "url": "https://research.draconitic.com/paper/6zd9b7h6b3crf",
  "venue": "The journal of physical chemistry. B",
  "versions": []
}