Sensory rhodopsin I photocycle intermediate SRI380 contains 13-cis retinal bound via an unprotonated Schiff base

AbstractSensory rhodopsin I (SRI), the mutated derivative SRI-D76N and the complex of SRI with its transducer HtrI were overexpressed in Halobacterium salinarium and analyzed by resonance Raman spectroscopy. In the initial state SRI contains all-trans retinal bound via a protonated Schiff base as confirmed by retinal extraction which yields 95 ± 3% all-trans retinal. The photocycle intermediate absorbing maximally at 380 nm (SRI380) contains a Schiff base linkage between the protein and 13-cis retinal. Extraction of illuminated SRI yields up to 93% 13-cis retinal. Neither the mutation D76N nor HtrI changed the vibrational pattern of the chromophore