Retinoid-binding proteins

The specific role of vitamin A in tissue differentiation has been an active area of research. The current thinking, developed in 1979, involves initial dehvery of retinol by holo-B >V (retinol-binding protein) to the cell cytosol (66). Retinol is then ultimately oxidized to retinoic acid and binds to a specific cellular retinoid-binding protein and is transported to the nucleus. Retinoic acid is then transferred to a nuclear retinoic acid receptor (RAR), which enhances the expression of a specific region of the genome. Transcription occurs and new proteins appear during the retinoic acid-induced differentiation of cells (56). 

Kang S, Duell EA, Fisher GJ, et al (1995) Application of retinol to human skin in vivo induces epidermal hyperplasia and cellular retinoid binding proteins characteristic of retinoic acid but without measurable retinoic acid levels or irritation. J Invest Dermatol 105 549-556... 

The interphotoreceptor retinoid-binding protein (Borst et al., 1989) functions in the regeneration of rhodopsin in the mammalian visual cycle. It is exclusive to vertebrates yet contains a repeated structure that has been found singly in bacterial and plant tail-specific proteases (TSPc) (Silber et al., 1992) and the archaeal tricorn protease (Tamura et al., 1996). The eukaryotic homologs of TSPc are likely to be inactive as... 

Nitrogen is not paramagnetic and does not offer the unique triplet state configuration that oxygen does (See Chapter 6). All of the data collected in conjunction with the retinoid binding proteins appears to point away from nitrogen as a participant in the chromophores of vision (See Chapter 7). 

The retinoids involved specifically in vision do not relate to the same chemical receptors as those found in the nutrition aspects of pharmacology. There is a different set of chemical receptors involved in the transport of retinol from the liver to the RPE cells of the retina. These receptors are found on the surface of the RPE cells and are specific for the retinoid binding proteins (RBP s) that transport the retinoids to the RPE. These RBP s play a unique role in the chromophore forming process that is not shared with the transport of retinol for purposes of metabolism and growth. Machlin says there are as many as 50,000 RBP receptor sites on the exposed surface of each RPE cell212. 

G10. Giguere, V., Retinoic acid receptors and cellular retinoid binding proteins Complex interplay in retinoic signalling. Endocr. Rev. 15, 61-79 (1994). 

Cellular Retinoid Binding Proteins CRBPs and CRABPs... 

There are five intracellular retinoid binding proteins that show considerable sequence homology not only with each other, but also with a variety of other intracellular binding proteins for hydrophobic metabolites, including the intracellular fatty acid binding protein (Li and Norris, 1996 Noy, 2000 Vogel et al., 2001). 

The pigment epithelium of the retina receives all- fraws-retinol fromplasma RBP. It is then isomerized to ll-c(s-retinol, which may either be stored as ll-c(s-retinyl esters or oxidized to ll-c(s-retinaldehyde, which is transported to the photoreceptor cells bound to an interphotoreceptor retinoid binding protein. 

Soprano DR (1994) Serum and cellnlar retinoid binding proteins. In Vitamin Receptors Vitamins and Ligands in Cell Communication, K Daksbinamurti (ed.), pp. 1-27. Cambridge, UK Cambridge University Press. 

McBee JK, KuksaV, Alvarez R, de Fera AR, Prezhdo O, Haeseleer F, Sokal I, and Palczewski K (2000) Isomerization of all-fra s-retinol to as-retinols in bovine retinal pigment epithelial cells dependence on the specificity of retinoid-binding proteins. Biochemistry 39,11370-80. 

Noy N (2000) Retinoid-binding proteins mediators of retinoid action. BiochemicalJour-nfl/348(Pt 3), 481-95. 

Tschanz CL and Noy N (1997) Binding of retinol in both retinoid-binding sites of interphotoreceptor retinoid-binding protein (IRBP) is stabilized mainly by hydrophobic mtetActiom,. Journal of Biological Chemistry 272,30201-7. 

Retinal antigens, such as S-antigen (arrestin), interphotoreceptor retinoid-binding protein (IRBP), rhodopsin, recoverin, and phosduscin, appear to hold uveitogenic properties. Immunization with these antigens or their fragments can induce... 

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