High impact information on RLBP1

• Staining with anti-CRALBP was found in two cell types in all species: the RPE and the Müller glial cell [1].
• This conversion is inhibited when 11-cis-retinol is in a complex with cellular retinaldehyde-binding protein (CRALBP), providing a clear demonstration of the protective effect of retinoid-binding proteins in retinoid processes in the eye, a function that has been long suspected but never proven [2].
• Preferential release of 11-cis-retinol from retinal pigment epithelial cells in the presence of cellular retinaldehyde-binding protein [3].
• Cellular retinaldehyde-binding protein (CRALBP) carries 11-cis-retinal and/or 11-cis-retinol as endogenous ligands in the retinal pigment epithelium (RPE) and Müller cells of the retina and has been linked with autosomal recessive retinitis pigmentosa [4].
• Cellular retinaldehyde-binding protein ligand interactions. Gln-210 and Lys-221 are in the retinoid binding pocket [4].

Biological context of RLBP1

• The complete amino acid sequence of CRALBP from bovine retina has been determined by direct microanalysis of the protein [5].
• These results provide a basis for a systematic higher resolution mutagenesis study directed toward correlating CRALBP structural domains with function [6].
• Nick-translated bovine CRALBP cDNA probes were then used to clone from a human retinal cDNA library a 1317-base pair cDNA encoding human CRALBP [7].
• Residues Gln-210 and Lys-221 are located within a region of CRALBP exhibiting sequence homology with the ligand binding cavity of yeast phosphatidylinositol-transfer protein [4].
• Buried and solvent-exposed lysine residues were identified in bovine CRALBP by reductive methylation of the holoprotein followed by denaturation and reaction with [3H]acetic anhydride [4].

Anatomical context of RLBP1

• However, CRALBP is also present in optic nerve and brain where its natural ligand and function are not yet known [4].
• In adult rat and mouse optic nerves, the CRALBP(+) somata showed the same distribution as oligodendrocytes [8].
• METHODS: An overlay assay was used to detect interactions of CRALBP with components of RPE microsomes [9].
• Immunoperoxidase cytochemistry and double labeling immunofluorescence revealed CRALBP(+) cells in brain that resembled oligondendrocytes and not astrocytes, microglial cells, or pinealocytes [8].
• Differential expression of the cellular retinaldehyde-binding protein in bovine ciliary epithelium [10].

Associations of RLBP1 with chemical compounds

• Cellular retinaldehyde-binding protein (CRALBP) carries 11-cis-retinol or 11-cis-retinaldehyde as endogenous ligands and may function as a substrate carrier protein that modulates interaction of these retinoids with visual cycle enzymes [6].
• The amino acid sequence deduced from the cDNA corresponds exactly to that determined by direct analysis of NH2-terminally acetylated bovine CRALBP (Crabb, J. W., Johnson, C. M., Carr, S. A., Armes, L. G., and Saari, J. C. (1988) J. Biol. Chem. 263, 18678-18687) [7].
• Localization of CRALBP in RPE corroborates previous biochemical studies; its presence in the Müller cell suggests that this glial cell may play a hitherto unsuspected role in vitamin A metabolism in retina [1].
• Ligand interactions determine the physiological role of CRALBP in the RPE where the protein is thought to function as a substrate carrier for 11-cis-retinol dehydrogenase in the synthesis of 11-cis-retinal for visual pigment regeneration [4].
• Procedures are described for labeling CRALBP with 9-cis-retinaldehyde, 11-cis-retinaldehyde, or 11-cis-retinol [11].

Physical interactions of RLBP1

• The quantum efficiency of photoisomerization for CRALBP X 11-cis-retinaldehyde was determined by comparing the rate of photoisomerization of 11-cis-retinaldehyde bound to purified CRALBP and opsin [12].
• Eleven-cis-retinol bound to CRALBP is a better substrate for esterification by microsomes from retinal pigment epithelium (RPE) than all-trans-retinol bound to cellular retinol-binding protein (CRBP) [13].

Other interactions of RLBP1

• 11-cis-Retinaldehyde bound to cellular retinaldehyde-binding protein (CRALBP) is unaffected in bovine eyecup preparations by illumination that bleaches approximately 70% of the rhodopsin [12].

Analytical, diagnostic and therapeutic context of RLBP1

• Topological and epitope mapping of the cellular retinaldehyde-binding protein from retina [6].
• Circular dichroism demonstrated that CRALBP had not been denatured by the photobleaching required for endogenous ligand removal [14].
• By immunoelectron microscopy, anti-bovine CRALBP labeling was restricted to the cytoplasm of both RPE and Muller cells, with light labeling of nuclear euchromatin in both cell types [15].
• Immunocytochemistry of CRALBP before and after cryopreservation in uncultured bovine RPE cells disclosed expression and reexpression of RPE cell marker protein [16].
• Using indirect immunofluorescence and frozen-sectioned bovine ciliary epithelium, CRALBP was localized to the pigmented ciliary epithelial cell layer along the entire ciliary epithelium [10].

References