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cellular retinol-binding protein 1 Cellular retinol-binding proteins (CRBPs) participate in the cellular uptake of vitamin A in the form of free retinol. Retinol achieves a higher chemical stability when bound to CRBPs, and its interaction with retinol-binding proteins allows the solubilization in the aqueous medium of the hydrophobic retinol molecule. There are four human CRBP types (CRBP1, -2, -3, -4) which differ in their tissue-specific expression pattern, as well as in their different ligand affinities. CRBP1 (also known as Retinol-Binding Protein 1, CRBP, RBPC, CRBP1, CRBPI, CRABP-I) is widely expressed in numerous tissues: it has highest abundance in the liver, kidney, lung, and retinal pigment epithelium cells of the eye. CRBP1 has a high affinity for retinol. It accepts retinol transported from the plasma to cytosol via a cell surface receptor named STRA6, which interacts with serum retinol-binding protein. CRBP1 can bind all-trans-retinol, all trans-retinal and 13-cis-retinol, but not 9-cis-retinol. CRBPs belong to the intracellular fatty acid-binding protein (FABP) family, members of which are small proteins that bind hydrophobic ligands in a non-covalent, reversible manner, and, besides CRBPS, include the cellular retinoic acid-binding proteins (CRABPs) and the fatty acid-binding proteins (FABPs). |
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