Characterization of a novel carotenoid cleavage dioxygenase from plants

The plant hormone abscisic acid is derived from the oxidative cleavage of a carotenoid precursor. Enzymes that catalyze this carotenoid cleavage react ion, nine-cis epoxy-carotenoid dioxygenases, have been identified in severa l plant species. Similar proteins, whose functions are not yet known, are p resent in diverse organisms, A putative cleavage enzyme from Arabidopsis th aliana contains several highly conserved motifs found in other carotenoid c leavage enzymes. However, the overall homology with known abscisic acid bio synthetic enzymes is low. To determine the biochemical function of this pro tein, it was expressed in Escherichia coil and used for in vitro assays. Th e recombinant protein was able to cleave a variety of carotenoids at the 9- 10 and 9'-10' positions. In most instances, the enzyme cleaves the substrat e symmetrically to produce a C-14 dialdehyde and two C-13 products, which v ary depending on the carotenoid substrate. Based upon sequence similarity, orthologs of this gene are present throughout the plant kingdom. A similar protein in beans catalyzes the same reaction in vitro. The characterization of these activities offers the potential to synthesize a variety of intere sting, natural products and is the first step in determining the function o f this gene family in plants.