Ancestral enzyme reconstruction to identify the evolutionary origin of the TCA cycle to be a carbon fixation pathway.

Research Project

Project/Area Number	17K15166
Research Category	Grant-in-Aid for Young Scientists (B)
Allocation Type	Multi-year Fund
Research Field	Evolutionary biology
Research Institution	The University of Tokyo
Principal Investigator	Kameya Masafumi 東京大学, 大学院農学生命科学研究科(農学部), 助教 (80748517)
Project Period (FY)	2017-04-01 – 2020-03-31
Project Status	Completed (Fiscal Year 2019)
Budget Amount *help	¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000) Fiscal Year 2019: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2018: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000) Fiscal Year 2017: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Keywords	TCA回路 / 祖先型酵素 / 代謝進化 / 炭酸固定 / 実験進化学
Outline of Final Research Achievements	Protein sequences of three ancestral enzymes were deduces by using those of extant enzymes that catalyzes two analogous reactions in the rTCA cycle. Genes encoding the ancestral enzymes were introduce to Escherichia coli and successfully expressed. The purified enzymes catalyzed the expected two reactions. This is the first experimental result that support author's hypothesis that the TCA cycle and the extant rTCA cycle evolved from a primitive rTCA cycle consisting of fewer number of enzymes.
Academic Significance and Societal Importance of the Research Achievements	TCA回路（別名クエン酸回路、Krebs回路）は、多くの生物の炭素代謝・エネルギー代謝の中心で働き、もっともよく知られた代謝経路と言える。しかし、本代謝系がどのようにして成立したか、その進化的起源は明らかでなかった。本研究では、TCA回路を逆回しにした炭酸固定代謝（rTCA回路）に着目し、TCA回路がrTCA回路から進化したという説を提唱すると共に、単純な酵素構成の系からより複雑で高活性な系への代謝進化という新たなモデルが示された。