Abstract
The visual cycle is the complex enzymatic retinoid-processing involved in regenerating bleached rod and cone visual pigments.1 Central to visual cycle physiology is the cellular retinaldehyde-binding protein (CRALBP), a 36kDa cytosolic protein with high affinity for 11-cis-retinal and 11-cis-retinol. CRALBP is expressed in retinal pigment epithelium (RPE) and Müller cells, as well as in ciliary epithelium, iris, cornea, pineal gland and a subset of oligodendrocytes of the optic nerve and brain.2 Its function outside the RPE is not known, although a recent behavioral genetic study suggests that CRALBP may contribute to ethanol preference in mice.3 In the RPE, CRALBP serves as an 11-cis-retinol acceptor in the visual cycle isomerization step and as a substrate carrier for 11-cis-retinol dehydrogenase. 4–8 These functions require the rapid association and release of retinoid from the CRALBP ligand-binding pocket and involve critical protein interactions. To better understand the visual cycle, we are characterizing CRALBP ligand and protein interactions and retinoid trafficking within the RPE.