Retinol-binding protein that mediates retinol transport in blood plasma (PubMed:5541771). Delivers retinol from the liver stores to the peripheral tissues (Probable). Transfers the bound all-trans retinol to STRA6, that then facilitates retinol transport across the cell membrane (PubMed:22665496). Interacts with TTR (PubMed:5541771, PubMed:7754382, PubMed:10052934, PubMed:19021760). Interaction with TTR prevents its loss by filtration through the kidney glomeruli (Probable). Interacts with STRA6 (PubMed:22665496, PubMed:25910211). Detected in blood plasma and in urine (at protein level). The disease is caused by variants affecting the gene represented in this entry. Loss of functional RBP4 protein results in serum retinol deficiency. Lack of normal levels of retinol impairs the visual cycle leading to night blindness at early stages; prolonged deficiency may lead to retinal degeneration. Additionally, retinol deficiency may result in dry skin, increased susceptibility to infection and acne (PubMed:23189188). The disease is caused by variants affecting the gene represented in this entry. Belongs to the calycin superfamily. Lipocalin family. Truncated N-terminus. Retina International's Scientific Newsletter Retinol-binding protein 4 entry