Femtosecond infrared spectroscopy of channelrhodopsin-1 chromophore isomerization

Vibrational dynamics of the retinal all-trans to 13-cis photoisomerization in channelrhodopsin-1 from Chlamydomonas augustae (CaChR1) was investigated by femtosecond visible pump mid-IR probe spectroscopy. After photoexcitation, the transient infrared absorption of C-C stretching modes was detected. The formation of the 13-cis photoproduct marker band at 1193 cm−1 was observed within the time resolution of 0.3 ps. We estimated the photoisomerization yield to (60 ± 6) %. We found additional time constants of (0.55 ± 0.05) ps and (6 ± 1) ps, assigned to cooling, and cooling processes with a back-reaction pathway. An additional bleaching band demonstrates the ground-state heterogeneity of retinal.