Methods for Producing Recombinant Human Cellular Retinaldehyde-Binding Protein

The cellular retinaldehyde-binding protein (CRALBP) is expressed at high levels in vertebrate visual trssue, where it may serve to modulate the interaction of 11-cis -retinol with visual-cycle enzymes in the retinal pigment epithelium (RPE) (1 ). This 36-kDa protein is remarkably stereo selective in recognizing the isomer of retinaldehyde mvolved in vision, and carries 11-cis -retinaldehyde or 11-cis -retinol as physiological ligands (2 ). Notably, retinoid bound to CRALBP is less susceptible to photo-isomerization than when bound to rhodopsin (3 ). In addition to RPE, the protein is expressed in Müller cells of the neural retina (4 ), ocular ciliary epithelium (5 , 6 ), and transiently in iris (7 ). Recent investigations show the protein is also expressed at lower levels in glia of the optic nerve and brain (8 ). While in vitro evidence suggests a substrate-routing function for CRALBP in RPE (1 ), the physiological role of CRALBP in vivo remains unconfirmed.