Functional genomics approach to the study of triterpene biosynthesis
Y. Ebizuka, Y. Katsube, T. Tsutsumi, T. Kushiro, and M. Shibuya
Graduate School of Pharmaceutical Sciences, The University
of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Abstract: The Arabidopsis thaliana genome-sequencing
project has identified the presence of 13 oxidosqualene cyclase homologs
in this plant. In addition to the already identified clones, namely,
CAS1 cycloartenol synthase, LUP1 lupeol synthase, and YUP8H12R.43 multifunctional
triterpene synthase, two new cDNAs of the putative oxidosqualene cyclase
genes, F1019.4 and T30F21.16, were obtained by polymerase chain reaction
(PCR) and functionally expressed in yeast. Liquid chromatography/mass
spectrometry (LC/MS) analysis led to the identification of some of their
reaction products. Interestingly, except for CAS1 for sterol biosynthesis
of primary metabolism, so-far-obtained all triterpene synthases of this
plant are multifunctional, producing more than one cyclization product.
A feeding experiment of 13C-labeled acetate with LUP1 lupeol
synthase transformant demonstrated the stereospecific water addition
to lupenyl cation intermediate, yielding 3b,20
dihydroxylupane, which accounts for the multiproduct nature of this
synthase.
*Pure Appl.Chem. 75,
141�419 (2003). An issue of reviews and research papers based on
lectures presented at the 23rd IUPAC International Symposium on the
Chemistry of Natural Products, Florence, Italy, 28 July � 2 August 2002.
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