Abstract: Folates, including tetrahydrofolate and its kinds of derivatives, belong to water soluble B family (B9). As key co-factors in one-carbon transfer reactions, folates take parts in several metabolic pathways in almost all organisms. 5-formyltetrahydrofolate cycloligase (5FCL) was reported to catalyze the storage form of 5-formyltetrahydrofolate (5-CHO-THF) into active folate forms. Here, maize 5FCL was cloned and characterized. Zm5FCL contained a conserved 5-formyltetrahydrofolate cyclo-ligase superfamily domain and had high sequence consistency with its homologues. The in-vitro enzymatic assay of recombinant Zm5FCL protein expressed in Escherichia coli cells showed that Zm5FCL had conserved function of converting 5-CHO-THF into 5,10-methenyltetrahydrofolate (5,10-CH=THF), and over-expression analysis of Zm5FCL in Arabidopsis 5fcl mutant demonstrated that Zm5FCL could convert 5-CHO-THF into 5,10-methenyltetrahydrofolate (5,10-CH=THF), and then 5-methyltetrahydrofolate (5-CH3-THF). These results suggested that Zm5FCL was involved in folate metabolism,which was presumed that Zm5FCL played important roles in maize folate metabolism.

Key words: folates, folate metabolism, 5-formyltetrahydrofolate cycloligase

摘要： 叶酸属于维生素B族（B9），包括四氢叶酸及其多种衍生物。叶酸作为一碳代谢的辅因子，参与生物体内的多种代谢活动。5-甲酰四氢叶酸环化连接酶（5FCL）催化贮存形式的叶酸衍生物5-甲酰四氢叶酸（5-CHO-THF）向代谢活跃的叶酸衍生物转化。对玉米5-甲酰四氢叶酸环化连接酶（Zm5FCL）进行基因克隆和功能分析，发现Zm5FCL蛋白包含保守的5-formyltetrahydrofolate cyclo-ligase superfamily结构域。通过将该蛋白在大肠杆菌中进行异源表达、纯化及体外酶活性分析，表明Zm5FCL能够催化5-CHO-THF向5,10-次甲基四氢叶酸（5,10-CH=THF）转化。进一步在拟南芥5fcl突变体中进行Zm5FCL过表达分析表明，Zm5FCL能够代谢突变体中的5-CHO-THF向5,10-CH=THF和5-甲基四氢叶酸（5-CH3-THF）的转化。上述结果表明Zm5FCL在叶酸代谢中执行保守的生物学功能，推测其在玉米叶酸代谢中发挥着重要作用。

关键词: 叶酸, 叶酸代谢, 5-甲酰四氢叶酸环化连接酶