| Title | The New beta -D-Glucosidase in Terpenoid-Isoquinoline Alkaloid Biosynthesis in Psychotria ipecacuanha. | | Author(s) | Nomura T, Quesada AL, Kutchan TM | | Institution | Donald Danforth Plant Science Center, St. Louis, Missouri 63132. | | Source | J Biol Chem 2008 Oct 16. | | Abstract | Ipecac alkaloids produced in the medicinal plant Psychotria ipecacuanha such as emetine and cephaeline possess monoterpenoid-tetrahydroisoquinoline skeleton, which is formed by condensation of dopamine and secologanin. Deglucosylation of one of the condensed products N-deacetylisoipecoside (1alpha(S)-epimer) is considered to be a part of the reactions for emetine biosynthesis, whereas its 1beta(R)-epimer N-deacetylipecoside is converted to ipecoside in P. ipecacuanha. Here, we isolated a cDNA clone Ipeglu1 encoding Ipecac alkaloid beta-D-glucosidase from P. ipecacuanha. The deduced protein showed 54% and 48% identities to raucaffricine beta-glucosidase and strictosidine beta-glucosidase, respectively. Recombinant IpeGlu1 enzyme preferentially hydrolyzed glucosidic Ipecac alkaloids except for their lactams, but showed poor or no activity toward other substrates including terpenoid-indole alkaloid glucosides. LC-MS/MS analysis of deglucosylated products of N-deacetylisoipecoside revealed spontaneous transitions of the highly reactive aglycons, one of which was supposed to be the intermediate for emetine biosynthesis. IpeGlu1 activity was extremely poor toward 7-O-methyl and 6,7-O,O-dimethyl derivatives. However, 6-O-methyl derivatives were hydrolyzed as efficiently as non-methylated substrates, suggesting the possibility of 6-O-methylation prior to deglucosylation by IpeGlu1. In contrast to the strictosidine beta-glucosidase that stereospecifically hydrolyzes 3alpha(S)-epimer in terpenoid-indole alkaloid biosynthesis, IpeGlu1 lacked stereospecificity for its substrates where 1beta(R)-epimers were preferred to 1alpha(S)-epimers, although ipecoside (1beta(R)) is a major alkaloidal glucoside in P. ipecacuanha, suggesting the compartmentalization of IpeGlu1 from ipecoside. These facts have significant implications for distinct physiological roles of 1alpha(S)- and 1beta(R)-epimers and for the involvement of IpeGlu1 in the metabolic fate of both of them. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 18927081 |
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