5,10-Methenyltetrahydrofolate Synthetase (MTHFS)

5,10-Methenyltetrahydrofolate synthetase (MTHFS; EC 6.3.3.2) catalyzes the ATP- and Mg(2+)-dependent conversion of 5-formyltetrahydrofolate (5-FTHF) to 5,10-methenyltetrahydrofolate (5,10-MTHF), which is subsequently interconverted into other reduced folates involved in 1-carbon metabolism. It is a 27-kD monomeric protein with a pI of 7.0.The deduced 203-amino acid protein contains a consensus ATP-binding site, a potential Mg(2+)-binding site, a sequence similar to a conserved sequence present in almost all enzymes using 10-FTHF as a substrate, and several consensus phosphorylation sites. The human and rabbit MHTFS proteins are 77% identical. Northern blot analysis of human tissues detected an approximately 0.9-kb MTHFS transcript that was expressed preferentially in liver.