CRBP2

CRBP2, or cellular retinol-binding protein 2, is a small cytosolic protein that binds retinol (vitamin A alcohol) and retinal with high affinity. It belongs to the family of cellular retinol-binding proteins that sequester and shuttle retinoids within cells, regulating their availability for storage, metabolism, and signaling. In humans and most mammals, CRBP2 expression is predominantly in the small intestine, especially in enterocytes, where it participates in dietary vitamin A absorption and metabolism.

Functionally, CRBP2 binds retinol released from dietary sources within the enterocyte and presents it to enzymes involved in retinoid processing. The CRBP2–retinol complex can be directed to lecithin retinol acyltransferase (LRAT) for esterification to retinyl esters, which are then stored or packaged into chylomicrons for lymphatic transport. CRBP2 also helps direct retinol toward pathways that generate other retinoids, including retinal and retinoic acid, thereby influencing local signaling and systemic vitamin A homeostasis. By modulating retinoid flux, CRBP2 contributes to efficient vitamin A absorption and helps limit potential retinoid toxicity.

Structure and expression: CRBP2 is a ~15–20 kDa cytosolic protein with a compact globular fold that contains a hydrophobic pocket for retinol binding. Its intestinal expression profile contrasts with the broader distribution of other retinol-binding proteins in different tissues.

Clinical relevance: Alterations in CRBP2 expression or function can impact intestinal vitamin A uptake and metabolism. Animal models lacking CRBP2 exhibit changes in intestinal retinoid processing, underscoring its physiological role in vitamin A homeostasis.