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oai:figshare.com:article/34021127 2026-09-29T04:14:38Z category_1 category_4 category_915 category_13 category_14 category_15 category_873 category_734 category_61 portal_63 item_type_6 month_year_09_2026

A Residue-Resolved Mechanism for Trapped-Twist Spectral Tuning in Cyanobacteriochromes Shun Kohase (25135112) Kazuhiro J. Fujimoto (2024749) Rei Narikawa (1522429) Takeshi Yanai (1487584) Biophysics Biochemistry Physical Sciences not elsewhere classified Genetics Molecular Biology Neuroscience Chemical Sciences not elsewhere classified Biological Sciences not elsewhere classified Developmental Biology separation using quantum engineering cbcr absorption calculated spectra reproduce – b linkage – b inter thermally stable states twist spectral tuning results establish trapped large blue shift r </ sub g </ sub protein electrostatics red mechanical geometry optimization twist tuning c – states similarly wave function truncates π trp655 dominates thr658 becomes ring torsion resolved mechanism photoexcitation converts level handles driven mechanism dihedral orientation dependent rewiring cyanobacteriochromes cyanobacteriochromes binding photoreceptors based excited Cyanobacteriochromes (CBCRs) are bilin-binding photoreceptors that photoconvert between long-lived, thermally stable states; in the red/green subfamily, photoexcitation converts the red-absorbing P_r state to the green-absorbing P_g state with a large blue shift. Here we quantify this P_r–P_g separation using quantum-mechanical/molecular-mechanical geometry optimization and wave function-based excited-state calculations. Calculated spectra reproduce the P_r–P_g trend and show that the shift is dominated by a P_g-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 P_r–P_g gap. Residue–chromophore interaction energies reveal state-dependent rewiring: Trp655 dominates in P_r and regulates the C–D dihedral orientation, whereas in P_g this role shifts to Ile691, and Thr658 becomes a major P_g-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. 2026-09-29T00:00:00Z Text Journal contribution 10.1021/acs.jpcb.6c05208.s001 https://figshare.com/articles/journal_contribution/A_Residue-Resolved_Mechanism_for_Trapped-Twist_Spectral_Tuning_in_Cyanobacteriochromes/34021127 CC BY-NC 4.0