CRBP

CRBP stands for cellular retinol-binding protein, a family of small cytosolic proteins that bind retinoids such as retinol (vitamin A alcohol) and retinal with high affinity. They function as intracellular chaperones that preserve retinoids from oxidation and modulate their intracellular trafficking and metabolism, influencing retinoid signaling.

Within cells, CRBPs deliver retinol to enzymes that convert it to active metabolites. They supply retinol to LRAT for esterification and to retinol dehydrogenases and retinaldehyde dehydrogenases that generate retinal and retinoic acid, respectively. By sequestering retinoids, they regulate enzyme access and help maintain vitamin A homeostasis.

Isoforms and expression: The best-characterized member is CRBP1, widely expressed in liver, kidney, adipose tissue, and other organs, and encoded by the RBP1 gene in humans. A smaller intestine–enriched isoform CRBP2 has been described and serves in dietary retinol uptake. Additional CRBP family members have been described in various species, with tissue-specific patterns.

Structure and evolution: CRBPs are small (~15–17 kDa) cytosolic proteins with a conserved binding pocket that accommodates retinol. They bind retinol and retinal with high affinity, and structural studies reveal a hydrophobic pocket and conformational changes upon ligand binding. The proteins are part of the broader retinoid-binding protein family that facilitates intracellular handling of vitamin A derivatives.

Clinical and research relevance: Altered CRBP expression or function can perturb intracellular retinoid metabolism and signaling, potentially affecting differentiation, lipid metabolism, and immune responses. Experimental models have explored roles in cancer and metabolic disorders, but precise clinical implications in humans remain under study.