Interaction between Retinal G Protein–coupled Receptor Opsin and Cellular Retinaldehyde–Binding Protein In Vitro

Abstract

Abstract: : Purpose: Our aim is to test the hypothesis that CRALBP is involved in the dissociation of 11–cis–retinal from RGR and that the 11–cis chromophore is transferred from RGR to CRALBP during illumination. Methods: Structural interaction between immunoaffinity–purified RGR and recombinant human CRALBP was investigated by affinity chromatography. Functional interaction between the two proteins was investigated by HPLC analysis of retinoids before and after light treatment. Results: The addition of CRALBP to RGR reproducibly increased the net production of 11–cis–retinal formed by photoisomerization by ∼6.5%. During illumination, 11–cis–retinal from irradiated RGR was transferred to CRALBP. The presence of CRALBP resulted in rapid photobleaching of RGR and allowed complete extraction of 11–cis–retinal without the addition of hydroxylamine. Without CRALBP, 11–cis–retinal remained tightly bound to RGR. BSA had no effect on the metabolism of 11–cis–retinal. Conclusions:These in vitro results support a potential role for CRALBP in the function of RGR in the light. CRALBP serves as an acceptor of 11–cis–retinol in the isomerization step of the rod visual cycle and also appears to serve as an acceptor of 11–cis–retinal from RGR–mediated photoisomerization. CRALBP may have an active role in the hydrolysis and release of the 11–cis chromophore from RGR.

Keywords: retinoids/retinoid binding proteins • retina: neurochemistry • protein purification and characterization