Retinoids in Mammals: A Crystallographic Perspective

Sa？etak Retinoids are involved in several essential processes in mammals, including vision, morphogenesis, spermatogenesis and maintenance of epithelial tissue. Since they are labile compounds, nearly insoluble in water, they are present in body fluids and within the cell bound to specific retinoid-binding proteins. In plasma, a single protein, called retinol-binding protein, delivers the alcoholic form of vitamin A from its store sites to target cells. In the cytoplasm, four different cellular retinol-binding proteins and two retinoic acid-binding proteins have been discovered and structurally characterized to date. Finally, two classes of nuclear receptors for retinoic acid isomers have been characterized. The structure/function relationship for several retinoid-binding proteins is discussed here