Structural insights into spectral tuning and retinal exchange in cone visual pigments
- Sayaka Ohashi
- Kota Katayama
- Asato Kojima
- Xuchun Yang
- Masahiro Fukuda
- Filippo Sacchetta
- Ryoji Suno
- Yukihiko Sugita
- Nipawan Nuemket
- Suhyang Kim
- Kazuhiro Kobayashi
- Hiroo Imai
- So Iwata
- Eriko Nango
- Takuya Kobayashi
- Takeshi Noda
- Massimo Olivucci
- Hideaki E. Kato
- Hideki Kandori
2026-06-25
Color vision in catarrhine primates relies on red-, green-, and blue-sensitive cone pigments that share an 11- cis -retinal chromophore but differ in absorption maxima. Red and green pigments arose by recent gene duplication and differ at only a few residues. Here, we report cryo–electron microscopy structures of red and green cone pigments from the cynomolgus macaque ( Macaca fascicularis ) integrated with low-temperature vibrational spectroscopy and quantum mechanical and molecular mechanical modeling. The red-green spectral shift is dominated by threonine 285, the hydroxyl dipole of which modulates chromophore electrostatics, whereas steric effects appear modest. We also identified membrane-facing lateral openings in cone pigments but not in inactive rhodopsin. Comparisons with active-state structures suggest activation-dependent gating, and mutational and spectroscopic analyses support a role for this opening in retinal uptake and rapid pigment regeneration.