RBP4/Retinol-Binding Protein 4 Antibody (423614)

Retinol (also known as vitamin A) is unstable and insoluble in the aqueous solution. However, retinol becomes quite stable and soluble in plasma due to its tight interaction with Retinol-binding Protein 4 (RBP4), also known as Plasma Retinol-binding Protein (1‑3). A prototypic member of the lipocalin superfamily, RBP4 has a beta ‑barrel structure with a well-defined cavity. It is secreted from the liver, a process requiring the availability of retinol. RBP4 delivers retinol from the liver to the peripheral tissues. In plasma, the RBP4-retinol complex interacts with transthyretin (TTR), also known as thyroxine-binding protein and prealbumin. The retinol-RBP4-TTR complex prevents the loss of RBP4 by filtration through the kidney and increases the stability of the retinol-RBP4 complex. Defects in RBP4 cause retinol-binding protein deficiency, which affects night vision. Serum RBP4 levels are elevated in insulin-resistant mice and humans with obesity and type 2 diabetes, implying that RBP4, an adipocyte-derived signal, may be a biomarker and a drug target for the two diseases. The amino acid sequence of mouse RBP4 is 99%, 86%, 83% and 75% identical to that of rat, human/chimpanzee, dog and chicken.