Abstract
Cyclic triterpenes constitute one of the most diverse groups of plant natural products. Besides the intriguing biochemistry of their biosynthetic pathways, plant triterpenes exhibit versatile bioactivities, including antimicrobial effects against plant and human pathogens. While prokaryotes have been extensively used for the heterologous production of other classes of terpenes, the synthesis of cyclic triterpenes, which inherently includes the two-step catalytic formation of the universal linear precursor 2,3-oxidosqualene, is still a major challenge. We thus explored the suitability of the metabolically versatile photosynthetic α-proteobacterium Rhodobacter capsulatus SB1003 and cyanobacterium Synechocystis sp. PCC 6803 as alternative hosts for biosynthesis of cyclic plant triterpenes. Therefore, 2,3-oxidosqualene production was implemented and subsequently combined with different cyclization reactions catalyzed by the representative oxidosqualene cyclases CAS1 (cycloartenol synthase), LUP1 (lupeol synthase), THAS1 (thalianol synthase) and MRN1 (marneral synthase) derived from model plant Arabidopsis thaliana. While successful accumulation of 2,3-oxidosqualene could be detected by LC-MS analysis in both hosts, cyclase expression resulted in differential production profiles. CAS1 catalyzed conversion to only cycloartenol, but expression of LUP1 yielded lupeol and a triterpenoid matching an oxidation product of lupeol, in both hosts. In contrast, THAS1 expression did not lead to cyclic product formation in either host, whereas MRN1-dependent production of marnerol and hydroxymarnerol was observed in Synechocystis but not in R. capsulatus. Our findings thus indicate that 2,3-oxidosqualene cyclization in heterologous phototrophic bacteria is basically feasible but efficient conversion depends on both the respective cyclase enzyme and individual host properties. Therefore, photosynthetic α-proteo- and cyanobacteria are promising alternative candidates for providing new bacterial access to the broad class of triterpenes for biotechnological applications.
Highlights
Plant secondary metabolites comprise a large variety of structurally divergent compounds that can serve as signaling molecules or as protecting agents against microbial pathogens, herbivorous attacks or plant competitors
R. capsulatus harbors the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway leading to the formation of isoprene units and thereof derived farnesyl pyrophosphate (FPP), which is a natural intermediate in biosynthesis of the tetraterpenes spheroidene and spheroidenone [20]
We have demonstrated the applicability of the two phototrophic bacteria R. capsulatus SB1003 and Synechocystis sp
Summary
Plant secondary metabolites comprise a large variety of structurally divergent compounds that can serve as signaling molecules or as protecting agents against microbial pathogens, herbivorous attacks or plant competitors (overview in [1]). Among these secondary metabolites, terpenoids including the cyclic plant-type triterpenes constitute one of the largest and most diverse groups exhibiting important functions in plant physiology and development. The linear triterpene precursor squalene plays a role in defense elicitation against herbivore attacks [2], the sterol cycloartenol is important for membrane functionality, plastid biogenesis and cell viability [3], β-amyrin is involved in root development [4], marneral affects general plant growth and development [5], and lupeol is essential for root nodule formation [6]. Antifertility effects of lupeol were recently demonstrated [14] and contraceptive application is discussed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
