Three Recently Diverging Duplicated Methyltransferases Exhibit Substrate-Dependent Regioselectivity Essential for Xantholipin Biosynthesis

Lingxin Kong, Qing Wang, Weinan Yang, Jufang Shen, Yan Li, Xiaoqing Zheng, Lu Wang, Yiwen Chu, Zixin Deng, Yit Heng Chooi, Delin You

Research output: Contribution to journalArticle

Abstract

Polycyclic xanthones are characterized by highly oxygenated, angular hexacyclic frameworks and exhibit diverse biological activities. Although many of them have been isolated and chemically synthesized, the detailed biosynthetic machinery awaits discovery. Recently, xanthone construction in the xantholipin (1) pathway was shown to involve cryptic demethoxylation. This suggested a rationale for the existence of three O-methyltransferase (OMT) genes in the gene cluster, although there are only two O-methyl groups in the structure of 1. Here, in vivo and in vitro analysis have been used to show that the three paralogous OMTs, XanM1-M3, introduce individual methyl groups at specific points in the biosynthetic pathway. Each OMT can to some extent take over the role of the other OMTs, although they exhibit highly substrate-dependent regiospecificity. In addition, phylogenetic analysis suggests their evolution from a common ancestor. Four putative ancestral proteins were constructed, and one of them performed all the functions of XanM1-M3, while the others possessed more limited catalytic functions. The results suggest that a promiscuous common ancestor may have been able to catalyze all three reactions prior to gene duplication and functional divergence. The characterization of XanM1-M3 expands the enzyme inventory for polycyclic xanthone biosynthesis and suggests novel directed evolution approaches to diversifying natural product pathways.

Original languageEnglish
Pages (from-to)2107-2115
Number of pages9
JournalACS Chemical Biology
Volume15
Issue number8
DOIs
Publication statusPublished - 21 Aug 2020

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