The Biochemical Characterization of Two Carotenoid Cleavage Enzymes from Arabidopsis Indicates That a Carotenoid-derived Compound Inhibits Lateral Branching

• Published in: The Journal of biological chemistry 2004-11, Vol.279 (45), p.46940-46945
• Main Authors: Schwartz, Steven H, Qin, Xiaoqiong, Loewen, Michele C
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis Proteins - chemistry; beta Carotene - chemistry; Carotenoids - chemistry; Catalysis; Chromatography, High Pressure Liquid; Chromatography, Thin Layer; Cloning, Molecular; Dioxygenases - chemistry; Escherichia coli - metabolism; Kinetics; Mass Spectrometry; Models, Chemical; Mutation; Oxygen - chemistry; Oxygenases - chemistry; Recombinant Proteins - chemistry; Signal Transduction; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M409004200

Enzymes that are able to oxidatively cleave carotenoids at specific positions have been identified in animals and plants. The first such enzyme to be identified was a nine- cis -epoxy carotenoid dioxygenase from maize, which catalyzes the rate-limiting step of abscisic acid biosynthesis. Similar enzymes are necessary for the synthesis of vitamin A in animals and other carotenoid-derived molecules in plants. In the model plant, Arabidopsis , there are nine hypothetical proteins that share some degree of sequence similarity to the nine- cis -epoxy carotenoid dioxygenases. Five of these proteins appear to be involved in abscisic acid biosynthesis. The remaining four proteins are expected to catalyze other carotenoid cleavage reactions and have been named carotenoid cleavage dioxygenases (CCDs). The hypothetical proteins, AtCCD7 and AtCCD8, are the most disparate members of this protein family in Arabidopsis . The max3 and max4 mutants in Arabidopsis result from lesions in AtCCD7 and AtCCD8 . Both mutants display a dramatic increase in lateral branching and are believed to be impaired in the synthesis of an unidentified compound that inhibits axillary meristem development. To determine the biochemical function of AtCCD7, the protein was expressed in carotenoid-accumulating strains of Escherichia coli . The activity of AtCCD7 was also tested in vitro with several of the most common plant carotenoids. It was shown that the recombinant AtCCD7 protein catalyzes a specific 9-10 cleavage of β-carotene to produce the 10 ▾-apo-β-carotenal (C 27 ) and β-ionone (C 13 ). When AtCCD7 and AtCCD8 were co-expressed in a β-carotene-producing strain of E. coli , the 13-apo-β-carotenone (C 18 ) was produced. The C 18 product appears to result from a secondary cleavage of the AtCCD7-derived C 27 product. The sequential cleavages of β-carotene by AtCCD7 and AtCCD8 are likely the initial steps in the synthesis of a carotenoid-derived signaling molecule that is necessary for the regulation lateral branching.