Thymidylate synthase–5-fluoro-2'-deoxyuridine-5'-monophosphate–5,10-methylene tetrahydrofolate ternary complex (TS–FdUMP–CH2THF complex)

The TYMS–5-FU–folate ternary complex is a stable, covalently bound molecular structure that forms the basis of the pharmacological activity of fluoropyrimidine-based chemotherapies. It consists of the enzyme thymidylate synthase (TYMS), the active metabolite of 5-fluorouracil known as 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP), and the essential cofactor 5,10-methylene tetrahydrofolate (Source: UniProt, P04818; PubMed, PMID: 11753232). Under normal physiological conditions, TYMS catalyzes the reductive methylation of dUMP to dTMP, a rate-limiting step in the production of thymidine required for DNA replication. When 5-FU is administered, FdUMP competes with dUMP for the active site of the enzyme; in the presence of the folate cofactor, a stable covalent bond is formed that locks the enzyme in an inactive state. This entrapment results in a depletion of intracellular dTMP pools, causing DNA synthesis arrest and subsequent apoptosis, a phenomenon often referred to as thymineless death (Source: StatPearls, 2023). The stability of this complex is a critical determinant of drug efficacy, which is why leucovorin is frequently co-administered to expand the folate pool and enhance complex formation in the treatment of colorectal and other solid tumors.

Other names

Thymidylate synthase ternary complexTS-FdUMP-folate complexTYMS-FdUMP-mTHF complex5-FU-inhibited thymidylate synthase complex

The complex represents the irreversible covalent inhibition of thymidylate synthase, where the drug metabolite FdUMP and the folate cofactor 5,10-methylene tetrahydrofolate trap the enzyme, preventing the conversion of dUMP to dTMP and leading to thymineless cell death (Source: StatPearls, 2023; PubMed, PMID: 15151950).