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Peer-reviewedCC BY-NC-NDThe journal of physical chemistry. B

A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes.

  • Shun Kohase1
  • Kazuhiro J Fujimoto1,2
  • Rei Narikawa3
  • Takeshi Yanai1,2
  1. 1Department of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya464-8601, Japan.
  2. 2Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furocho, Chikusa, Nagoya464-8601, Japan.
  3. 3Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo192-0397, Japan.
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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.

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Cite

BibTeXRIS
BibTeX
@article{kohase2026residueresolved,
  title = {{A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes.}},
  author = {Shun Kohase and Kazuhiro J Fujimoto and Rei Narikawa and Takeshi Yanai},
  journal = {The journal of physical chemistry. B},
  year = {2026},
  month = oct,
  doi = {10.1021/acs.jpcb.6c05208},
  url = {https://europepmc.org/article/MED/42916730},
  note = {CC BY-NC-ND},
}
RIS
TY  - JOUR
TI  - A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes.
AU  - Shun Kohase
AU  - Kazuhiro J Fujimoto
AU  - Rei Narikawa
AU  - Takeshi Yanai
PY  - 2026
DA  - 2026/10/01
JO  - The journal of physical chemistry. B
DO  - 10.1021/acs.jpcb.6c05208
UR  - https://europepmc.org/article/MED/42916730
AB  - 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.
SN  - 1520-6106
SN  - 1520-5207
ER  -