Thymidylate synthase

Function

Thymidylate synthase (TS) catalyzes the methylation of dUMP to dTMP using 5,10-methylenetetrahydrofolate as a cofactor. TS is essential for DNA replication and repair^[2]. In protozoa, dihydrofolate reductase (DHFR) and TS are expressed as a bifunctional monomeric enzyme (DHFR-TS) with the DHFR entity at the N terminal. DHFR and TS catalyze consecutive reactions in the dTMP biosynthesis. There are two different types of TS – ThyA and ThyX. The types differ in their activity and structure. The TS ThyX are flavin-dependent enzymes.

Relevance

TS inhibition at its folate-binding site is used in anticancer therapeutic drugs. DHFR-TS inhibitors are potential drug targets against parasite-transferred diseases. TS exhibits oncogene-like activity.^[3]

Due to its role in cell division, thymidylate synthase has become a popular target for anticancer drugs. Indirect inhibition of thymidylate synthase by the drug 5-fluorouracil (5-FU) is one of the most used inhibitors for study of TS function. This drug indirectly inhibits TS as it it eventually converted to FdUMP, which forms a covalent complex with both the active site cysteine and CH₂H₄F. Inhibition of TS halts the production of dTMP and, indirectly, 2'-deoxythymidine-5'-triphosphate (dTTP). Both dTMP and dTTP are essential building blocks for DNA synthesis and their absence halts the ability of cells to replicate their genetic information. This is especially effective in cancer cells that rapidly divide and require large amounts of dTMP and dTTP. ^[4]

Structural highlights

TS ^[5]. Water molecules are shown as red spheres.

The active site Cysteine has two . Conformation 1 shows the active site cysteine bound to the intermediate 3.84 Angstroms away from the C6 carbon of the dNMP ring. Conformation 2 shows the active site cysteine unbound to the intermediate 4.21 Angstroms away from the C6 carbon of the dNMP ring.

3D structures of thymidylate synthase

Thymidylate synthase 3D structures