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Researchers Reveal Catalytic Mechanism of Triterpene Diversity in Plant

Mar 13, 2018     Email"> PrintText Size

Many terpenoids play important roles in plant growth and development, and adaptation to the environments. There are over 20, 000 terpenoids with known structures.

Triterpenoids are the major bioactive compositions for medicine plants. Plant 2, 3-oxidosqualene cyclases (OSC) is the key metabolic diverse enzyme that catalyze 2,3-oxidosqualene into more than 100 triterpene skeletons with different conformation and divergent structures. Despite the intensive study on OSC enzyme family, the mechanism of rising diverse triterpenes is not well understood.

In previous studies, Prof. QI Xiaoquan's group at Institute of Botany of Chinese Academy of Sciences has reported that parkeol synthase (OsPS), an OSC from japonica subspecies of cultivated rice (Oryza sativa L.), synthsizes a tetracyclic parkeol with Chair-Boat-Chair (C-B-C) conformation.

Recently, Prof. QI's group, collaborating with Prof. Anne Osbourn at John Innes Centre, UK, demonstrated that the ortholog gene encoding a novel promiscuous OSC, orysatinol synthase (OsOS), was characterized from indica subspecies of rice, and revealed that OsOS synthesizes a novel Chair-Semi-Chair-Chair (C-sC-C) conformational pentacyclic triterpene orysatinol as its main product and over 12 different other triterpenes.

The OsOS genes are widely distributed in indica subspecies of cultivated rice and in wild rice accessions with AA genome, while OsPS genes only sustained in japonica subspecies and its related wild species.

Through phylogenetic, molecular evolution, protein structure and biochemical analyses, the researchers identified three key amino acid residues amongst 46 polymorphic sites that determine functional conversion between OsPS and OsOS, specifically, the C-sC-C and C-B-C conformation interchanges. The different orientation of a fourth amino acid residue Tyr257 was shown to be important for functional conversion.

Besides, they discovered several new triterpenes including orysatinol, and revealed the mechanistic insights into the cyclization of 2,3-oxidosqualene into tetra- and pentacyclic skeletons with C-B-C and C-sC-C conformations, which provided useful information for the design of a specific triterpene synthase when synthetic biology strategy is applied to produce commercial active triterpeniods.

This study was published in New Phytologist. It was supported by the National Natural Science Foundation of China, China Scholarship Council, and Biotechnology and Biological Sciences Research Council.


(Editor: LIU Jia)


QI Xiaoquan

Institute of Botany

E-mail: xqi@ibcas.ac.cn

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