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Description

Retinaldehyde-binding protein 1 (UniProt P12271, also known as Cellular retinaldehyde-binding protein) is encoded by the RLBP1 (also known as CRALBP) gene (Gene ID 6017) in human. CRALBP is a retinoid-binding protein expressed in retinal pigment epithelial (RPE) cells and Mueller glia involved in the retinal visual cycle. Photoactivation of a visual pigment molecule in vertebrate rod and cone photoreceptors renders the pigment molecule into a bleached all-trans retinal form, which must be exported out of the photoreceptors to be converted back to the light-sensitive 11-cis retinal form in RPE cells (for both rods and cones) or in retinal Mueller glia (for cones only). The 11-cis chromophore is then imported back into photoreceptors, where it combines with a free opsin to regenerate the visual pigment. CRALBP is a 36 kDa water-soluble protein that facilitates the intracellular transport of hydrophobic 11-cis retinoids. Mutations in human RLBP1 cause several autosomal recessive retinal diseases, such as retinitis pigmentosa, Bothnia dystrophy, retinitis punctata albescens, fundus albipunctatus, and Newfoundland rod-cone dystrophy. Likewise, Rlbp1-knockout mice exhibit M-opsin mislocalization, M-cone loss, and impaired cone-driven visual behavior and light responses. Viral expression of CRALBP in Mueller cells, but not RPE cells, is reported to rescue the retinal visual cycle and M-cone sensitivity in Rlbp1-knockout mice.