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cellular retinol-binding protein 4 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. This group includes human CRBP4 (also known as retinoid-binding protein 7, CRABP4, CRBP4, CRBPIV) which is expressed primarily in kidney, heart, and transverse colon, and mouse CRBP4 which is highly expressed in white adipose tissue and mammary gland. Human CRBP4 binds retinol with an affinity lower than those for CRBP1, -2, -3. 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). |
Jiyao W et al.(2023). "The conserved domain database in 2023.",