This family represents the N-terminal hydrolase domain of the bifunctional protein 10-formyltetrahydrofolate dehydrogenase (FDH). This domain contains a 10-formyl-tetrahydrofolate (10-formyl-THF) binding site and shares sequence homology and structural topology with other enzymes utilizing this substrate. This domain functions as a hydrolase, catalyzing the conversion of 10-formyl-THF, a precursor for nucleotide biosynthesis, to tetrahydrofolate (THF). The overall FDH reaction mechanism is a coupling of two sequential reactions, a hydrolase and a formyl dehydrogenase, bridged by a substrate transfer step. The N-terminal hydrolase domain removes the formyl group from 10-formyl-THF and the C-terminal NADP-dependent dehydrogenase domain then reduces the formyl group to carbon dioxide. The two catalytic domains are connected by a third intermediate linker domain that transfers the formyl group, covalently attached to the sulfhydryl group of the phosphopantetheine arm, from the N-terminal domain to the C-terminal domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",