[3P-1] ポスター3（3P-01ー3P-47）

[3P-27] 立体構造に基づくSphingobium sp. SYK-6 由来MTHFRの機能解析

^○于 宏洋^1,2, 桑原 直之¹, 上村 直史³, 加藤 諒³, 千田 美紀¹, 政井 英司³, 千田 俊哉^1,2 (1.構造生物学研究センター・高エネ研, 2.総研大, 3.長岡技術科学大学)

Evolutionary adaptations of enzymes are frequently observed under extreme environments but rarely reverse the enzyme reactivity. MethyleneH4folate reductase (MTHFR) has been considered to catalyze the reduction of CH2-THF to methylH4folate (CH3-THF) in cells. However, MTHFR from Sphingobium sp. SYK-6 (S6MTHFR), which can utilize small molecular weight lignin such as vanillate as a sole carbon source, seems to catalyze the reverse reaction. In S. SYK-6, CH3-THF is generated by demethylation of vanillate, and the resultant CH3-THF is converted into CH2-THF by S6MTHFR for the 1C metabolism. To understand the molecular mechanism of the unique catalytic reaction of S6MTHFR, we biochemically and structurally analyzed S6MTHFR. As expected, S6MTHFR only catalyzes the oxidation of CH3-THF. Structure-based mutational analysis revealed that L48, F215, C219, and F269 form a specific binding site of CH3-THF. Conversely, NADH, which serves as a hydride donor in the typical MTHFR, is hampered accessing the active site by L48 and P49. Interestingly, the above-described residues are conserved among S6MTHFR homologs, suggesting that these homologs form a new class in the MTHFR family with the reverse catalytic reaction.