Retinol Binding Protein

The complex of retinol with its carrier protein,retinol-binding protein(RBP)has been crystallized and its three-dimensional structure determined using X-ray crystallography. Its most striking feature is an eight-stranded up-and-down beta barrel core that completely encapsulates the retinol molecule. Retinol-binding protein transports vitamin A in the plasma. It contains 182 amino acids (Mr 24218) and consists of eight anti-parallel beta-strands (A-H) that fold to form an orthogonal barrel. The loop connecting the strands A and B, C, and D,and E. The retinol molecule is found deep inside this barrel. Apart from its specific interaction with retinol, RBP is involved in two other molecular-recognition properties, that is it binds to transthyretin(TTR), another serum protein, and to a cell-surface receptor.