Cytochrome P450s (P450) play a key role in oxidative reactions in plant secondary metabolism. Some of them, which catalyze unique reactions other than the standard hydroxylation, increase the structural diversity of plant secondary metabolites. In isoquinoline alkaloid biosyntheses, several unique P450 reactions have been reported, such as methylenedioxy bridge formation, intramolecular C-C phenol-coupling and intermolecular C-O phenol-coupling reactions. We report here the isolation and characterization of a C-C phenol-coupling P450 cDNA (CYP80G2) from an expressed sequence tag library of cultured Coptis japonica cells. Structural analysis showed that CYP80G2 had high amino acid sequence similarity to Berberis stolonifera CYP80A1, an intermolecular C-O phenol-coupling P450 involved in berbamunine biosynthesis. Heterologous expression in yeast indicated that CYP80G2 had intramolecular C-C phenol-coupling activity to produce (S)-corytuberine (aporphine-type) from (S)-reticuline (benzylisoquinoline type). Despite this intriguing reaction, recombinant CYP80G2 showed typical P450 properties: its C-C phenol-coupling reaction required NADPH and oxygen and was inhibited by a typical P450 inhibitor. Based on a detailed substrate-specificity analysis, this unique reaction mechanism and substrate recognition were discussed. CYP80G2 may be involved in magnoflorine biosynthesis in C. japonica, based on the fact that recombinant C. japonica S-adenosyl-L-methionine:coclaurine N-methyltransferase could convert (S)-corytuberine to magnoflorine.Isoquinoline alkaloids are a large group of alkaloids and include many pharmacologically useful compounds; e.g. the analgesic morphinan alkaloid morphine, the anti-tussive alkaloid codeine, and the anti-microbial alkaloids berberine and sanguinarine. Due to the importance of these pharmaceutically useful alkaloids, their biosynthetic pathways have been well investigated, and several of them have been completely clarified at the enzyme level (1-3). It is now known that many isoquinoline alkaloids share a common biosynthetic pathway from L-tyrosine to the key intermediate (S)-reticuline.(S)-Reticuline is a central precursor of various types of isoquinoline alkaloids such as morphinans, aporphines, pavines, protoberberines, protopines, and benzophenanthridines (1, 4). Although the molecular origin of this chemical diversity has not yet been clarified, recent studies have shown that many of their oxidative steps are catalyzed by cytochrome P450s (P450) 2 ( Fig. 1) (1-3, 5-11). Members of the P450 family are found in a very large number of species, especially in the plant kingdom (246 and 356 species in Arabidopsis thaliana and Oryza sativa in contrast to 57 and 84 species in human and Drosophila melanogaster) (12, 13), and many of them have been shown to be involved in plant secondary metabolism (14, 15).In the biosyntheses of isoquinoline alkaloids, P450-mediated hydroxylation, methylenedioxy bridge formation, and phenolcoupling reactions have been reported. Although members of the CYP80B s...

(S)-Norcoclaurine is the entry compound in benzylisoquinoline alkaloid biosynthesis and is produced by the condensation of dopamine and 4-hydroxyphenylacetaldehyde (4-HPAA) by norcoclaurine synthase (NCS) (EC 4.2.1.78). Although cDNA of the pathogenesis-related (PR) 10 family, the translation product of which catalyzes NCS reaction, has been isolated from Thalictrum flavum, its detailed enzymological properties have not yet been characterized. We report here that a distinct cDNA isolated from Coptis japonica (CjNCS1) also catalyzed NCS reaction as well as a PR10 homologue of C. japonica (CjPR10A). Both recombinant proteins stereo-specifically produced (S)-norcoclaurine by the condensation of dopamine and 4-HPAA. Because a CjNCS1 cDNA that encoded 352 amino acids showed sequence similarity to 2-oxoglutarate-dependent dioxygenases of plant origin, we characterized the properties of the native enzyme. Sequence analysis indicated that CjNCS1 only contained a Fe 2؉ -binding site and lacked the 2-oxoglutarate-binding domain. In fact, NCS reaction of native NCS isolated from cultured C. japonica cells did not depend on 2-oxoglutarate or oxygen, but did require ferrous ion. On the other hand, CjPR10A showed no specific motif. The addition of o-phenanthroline inhibited NCS reaction of both native NCS and recombinant CjNCS1, but not that of CjPR10A. In addition, native NCS and recombinant CjNCS1 accepted phenylacetaldehyde and 3,4-dihydroxyphenylacetaldehyde, as well as 4-HPAA, for condensation with dopamine, whereas recombinant CjPR10A could use 4-hydroxyphenylpyruvate and pyruvate in addition to the above aldehydes. These results suggested that CjNCS1 is the major NCS in C. japonica, whereas native NCS extracted from cultured C. japonica cells was more active and formed a larger complex compared with recombinant CjNCS1.Higher plants produce divergent chemicals such as alkaloids, terpenoids, and phenolic compounds in secondary metabolism. Among these chemicals, alkaloids are very important in medicine because of their high biological activities. Alkaloids are low molecular weight, nitrogen-containing compounds that are found in ϳ20% of plant species. Most alkaloids are derived from amines produced by the decarboxylation of amino acids such as histidine, lysine, ornithine, tryptophan, and tyrosine. Although the coupling of amines to other products is the first important step in producing diverse alkaloids, this entry reaction has been poorly characterized. (S)-Strictosidine is a central intermediate for indole alkaloids. Strictosidine synthase, which catalyzes the formation of (S)-strictosidine from tryptamine and secologanin, is a rare exception in that its cDNA has been cloned from Catharanthus roseus and Rauvolfia serpentine (1, 2).Benzylisoquinoline alkaloids are a large and diverse group of pharmaceutical alkaloids with ϳ2,500 defined structures. Norcoclaurine produced from tyrosine is a key entry compound from which various benzylisoquinoline alkaloids such as analgesic morphine, colchicines, antibacterial berberine...

Higher plants produce structurally divergent chemicals, such as terpenoids, phenylpropanoids, and alkaloids [1]. Throughout human history, several plant materials have been used in natural medicines because of the pharmacological activities of these chemicals.Isoquinoline alkaloids are a large group of alkaloids, and include many pharmacologically useful compounds,

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