Identification of key amino acid residues determining product specificity of 2,3-oxidosqualene cyclase in Oryza species

Xue, Zheyong, Tan, Zhengwei, Huang, Ancheng, Zhou, Yuan, Sun, Juncong, Wang, Xiaoning, Thimmappa, Ramesha B., Stephenson, Michael J. ORCID: https://orcid.org/0000-0002-2594-1806, Osbourn, Anne and Qi, Xiaoquan (2018) Identification of key amino acid residues determining product specificity of 2,3-oxidosqualene cyclase in Oryza species. New Phytologist, 218 (3). pp. 1076-1088. ISSN 0028-646X

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Abstract

Triterpene synthases, also known as 2,3-oxidosqualene cyclases (OSCs), synthesize diverse triterpene skeletons that form the basis of an array of functionally divergent steroids and triterpenoids. Tetracyclic and pentacyclic triterpene skeletons are synthesized via protosteryl and dammarenyl cations, respectively. The mechanism of conversion between two scaffolds is not well understood. Here, we report a promiscuous OSC from rice (Oryza sativa) (OsOS) that synthesizes a novel pentacyclic triterpene orysatinol as its main product. The OsOS gene is widely distributed in indica subspecies of cultivated rice and in wild rice accessions. Previously, we have characterized a different OSC, OsPS, a tetracyclic parkeol synthase found in japonica subspecies. Phylogenetic and protein structural analyses identified three key amino acid residues (#732, #365, #124) amongst 46 polymorphic sites that determine functional conversion between OsPS and OsOS, specifically, the chair–semi(chair)–chair and chair–boat–chair interconversions. The different orientation of a fourth amino acid residue Y257 was shown to be important for functional conversion. The discovery of orysatinol unlocks a new path to triterpene diversity in nature. Our findings also reveal mechanistic insights into the cyclization of oxidosqualene into tetra- and pentacyclic skeletons, and provide a new strategy to identify key residues determining OSC specificity.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 27 Sep 2022 09:30
Last Modified: 25 Oct 2022 00:15
URI: https://ueaeprints.uea.ac.uk/id/eprint/88660
DOI: 10.1111/nph.15080

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