In enzymology, a 5-formyltetrahydrofolate cyclo-ligase (EC 6.3.3.2) is an enzyme that catalyzes the chemical reaction

ATP + 5-formyltetrahydrofolate (folinic acid) ${\displaystyle \rightleftharpoons }$ ADP + phosphate + 5,10-methenyltetrahydrofolate

Thus, the two substrates of this enzyme are ATP and 5-formyltetrahydrofolate, whereas its 3 products are ADP, phosphate, and 5,10-methenyltetrahydrofolate.

This enzyme belongs to the family of ligases, specifically the cyclo-ligases, which form carbon-nitrogen bonds. The systematic name of this enzyme class is 5-formyltetrahydrofolate cyclo-ligase (ADP-forming). Other names in common use include 5,10-methenyltetrahydrofolate synthetase (MTHFS), formyltetrahydrofolic cyclodehydrase, and 5-formyltetrahydrofolate cyclodehydrase. This enzyme participates in one carbon pool by folate.

Structural studies

As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes 1SBQ, 1SOU, 1U3F, 1U3G, and 2JCB.

Role in pathology

Mutations of the MTHFS gene cause the disease 5,10-methenyltetrahydrofolate synthetase deficiency.