Cloning and characterization of a human beta,beta-carotene-15, 15 '-dioxygenase that is highly expressed in the retinal pigment epithelium

Retinoids play a critical role in vision, as well as in development and cel lular differentiation. beta,beta -Carotene-15,15'-dioxygenase (Bcdo), the e nzyme that catalyzes the oxidative cleavage of beta,beta -carotene into two retinal molecules, plays an important role in retinoid synthesis. We repor t here the first cloning of a mammalian Bcdo, Human BCDO encodes a protein of 547 amino acid residues that demonstrates 68% identity with chicken Bcdo , It is expressed highly in the retinal pigment epithelium (RPE) and also i n kidney, intestine, liver, brain, stomach, and testis, The gene spans appr oximately 20 kb, is composed of 11 exons and 10 introns, and maps to chromo some 16q21-q23, A mouse orthologue was also identified, and its predicted a mino acid sequence is 83% identical with human BCDO, Biochemical analysis o f baculovirus expressed human BCDO demonstrates the predicted beta,beta -ca rotene-15,15'-dioxygenase activity. The expression pattern of BCDO suggests that it may provide a local supplement to the retinoids available to photo receptors, as well as a supplement to the retinoid pools utilized elsewhere in the body. In addition, the finding that many of the enzymes involved in retinoid metabolism are mutated in retinal degenerations suggests that BCD O may also be a candidate gene for retinal degenerative disease, (C) 2001 A cademic Press.