Identification of a Unique Germacrene A Oxidase from Xanthium strumarium

Abstract

8,12-sesquiterpene lactones (STLs) are an important class of natural products with unique pharmaceutical activities. For years the pathway leading to 8,12-STLs remains an enigma. Xanthium strumarium accumulates abundant 8,12-STLs, and xanthatin is a characteristic 8,12-STL in it. Xanthatin has been previously postulated to be derived from germacrene A, but the steps from germacrene A to xanthatin are unknown. As part of an effort to understand the xanthatin biosynthetic pathway. This study reports the characterization of a unique germacrene A oxidase (XsGAO) from X. strumarium. Unlike a classical GAO enzyme, which is known to catalyze a three-step oxidation of germarene A to yield germacrene A acid (GAA), surprisingly, XsGAO catalyzed only one-step conversion of germacrene A to germacrene A alcohol. We discussed that GAO may be pressured to acquire a novel activity during the evolutionary path for the biosynthesis of 8,12-STLs.

Cloning and Functional Characterization of Two Germacrene A Oxidases Isolated from Xanthium sibiricum

“…GAO isolated from L. sativa was expressed in an engineered yeast to synthesize GAA de novo, and the classical GAO activity involved three-step oxidation of germacrene A (GA) to yield GAA and 12,6-guaianolides [ 25 , 34 ], similar to N. benthamiana [ 35 ]. Meanwhile, an Xs GAO from X. strumarium catalyzed only one-step conversion of germacrene A to germacrene alcohol [ 36 ], but this study clearly shows that Xs GAO1 and Xs GAO2 catalyzed a second step of oxidation of the non-natural substrate germacrene A to germacrene A acid, which was not observed in yeast with a different GAO. Apparently, Xs GAO2 is a unique enzyme, a functional adaption of SLTs’ biosynthetic pathway diversification.…”

Antibacterial and anthelmintic activities of Xanthium strumarium (Asteraceae) extracts

“…An important class of natural products with a unique pharmaceutical activity is 8,12-sesquiterpene lactones (STLs). Zheng et al (2022) reported about a unique germacrene А oxidase (XsGAO) from X. strumarium. Unlike the classic enzyme GAO, which catalyzes the three-stage oxidation of germacrene А with formation of germacrene acid A (GAA), XsGAO catalyzes only one-stage transformation of germacrene into germacrene alcohol (Zheng et al, 2022).…”

“…Zheng et al (2022) reported about a unique germacrene А oxidase (XsGAO) from X. strumarium. Unlike the classic enzyme GAO, which catalyzes the three-stage oxidation of germacrene А with formation of germacrene acid A (GAA), XsGAO catalyzes only one-stage transformation of germacrene into germacrene alcohol (Zheng et al, 2022). Sahu et al (2010) evaluated the pharmaceutical properties of the leaves of X. strumarium, finding that alcohol extract exerted a significant anti-inflammatory, anesthetic, and antimicrobial actions.…”