A lycopene -cyclase/lycopene epsilon-cyclase/light-harvesting complex-fusion protein from the green alga Ostreococcus lucimarinus can be modified to produce -carotene and -carotene at different ratios

作者：Blatt Andreas; Bauch Matthias E; Poerschke Yvonne; Lohr Martin^*

来源：Plant Journal, 2015, 82(4): 582-595.

DOI：10.1111/tpj.12826

• Ostreococcus lucimarinus
• Mamiellales
• carotenoid biosynthesis
• lycopene cyclase
• Chlamydomonas reinhardtii
• light-harvesting complex
• Bigelowiella natans

Biosynthesis of asymmetric carotenoids such as -carotene and lutein in plants and green algae involves the two enzymes lycopene -cyclase (LCYB) and lycopene epsilon-cyclase (LCYE). The two cyclases are closely related and probably resulted from an ancient gene duplication. While in most plants investigated so far the two cyclases are encoded by separate genes, prasinophyte algae of the order Mamiellales contain a single gene encoding a fusion protein comprised of LCYB, LCYE and a C-terminal light-harvesting complex (LHC) domain. Here we show that the lycopene cyclase fusion protein from Ostreococcus lucimarinus catalyzed the simultaneous formation of -carotene and -carotene when heterologously expressed in Escherichia coli. The stoichiometry of the two products in E.coli could be altered by gradual truncation of the C-terminus, suggesting that the LHC domain may be involved in modulating the relative activities of the two cyclase domains in the algae. Partial deletions of the linker region between the cyclase domains or replacement of one or both cyclase domains with the corresponding cyclases from the green alga Chlamydomonas reinhardtii resulted in pronounced shifts of the -carotene-to--carotene ratio, indicating that both the relative activities of the cyclase domains and the overall structure of the fusion protein have a strong impact on the product stoichiometry. The possibility to tune the product ratio of the lycopene cyclase fusion protein from Mamiellales renders it useful for the biotechnological production of the asymmetric carotenoids -carotene or lutein in bacteria or fungi.
Significance Statement We have studied an unusual fusion of two competing carotenoid biosynthetic enzymes and a light-harvesting domain occurring in a largely unexplored yet important group of marine green algae. The results suggest the light-harvesting domain to play a decisive role in the tug of war between the competing lycopene cyclases and open a new way for the biotechnological production of high-value carotenoids such as alpha-carotene and lutein.

• 出版日期2015-5