This family includes the 5,10-methylenetetrahydrofolate reductase EC:1.7.99.5 from bacteria and methylenetetrahydrofolate reductase EC: 1.5.1.20 from eukaryotes. The structure for this domain is known [1] to be a TIM barrel.

1: The structure and properties of methylenetetrahydrofolate reductase from Escherichia coli suggest how folate ameliorates human hyperhomocysteinemia [see comments] Guenther BD, Sheppard CA, Tran P, Rozen R, Matthews RG, Ludwig ML; Nat Struct Biol 1999;6:359-365. PMID:10201405