1.A.3. (ii) Anabaena sensory rhodopsin

　　Anabaena sensory rhodopsin (ASR) is a microbial rhodopsin in the cyanobacterium sp. PCC7120, and has been suggested to regulate cell processes in a light-quality-dependent manner (color-discrimination) through interaction with a water-soluble transducer protein (Tr). However, light-dependent ASR-Tr interaction changes have not yet to be demonstrated. We applied the transient grating (TG) method to investigate protein−protein interaction between ASR with Tr. The molecular diffusion component of the TG signal upon photostimulation of ASRAT (ASR with an all-trans retinylidene chromophore) revealed that Tr dissociates from ASR upon formation of the M-intermediate and rebinds to ASR during the decay of M; i.e. light induces transient dissociation of ASR and Tr during the photocycle. Further correlating the dissociation of the ASR-Tr pair with the M-intermediate, no transient dissociation was observed after the photoexcitation of the blue-shifted ASR13C (ASR with 13-cis, 15-syn chromophore), which does not produce M. This distinction between ASRAT and ASR13C, the two isomeric forms in a color-sensitive equilibrium in ASR, provides a potential mechanism for color-sensitive signaling by ASR.





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