C1‐ Tetrahydrofolate Synthase Contribution to 1C Metabolism

Abstract

Folate‐dependent one‐carbon (1C) metabolism is required for the de novo synthesis of thymidylate, purines, and methionine. Impairments in 1C metabolism result from inadequate intake of folate and other B‐vitamins, polymorphisms in folate‐utilizing genes, physiological states such as cancer and pregnancy, and the interaction among these factors. Although impaired 1C metabolism is associated with these pathologies, the mechanisms and causal pathways have not been established. Recent studies have shown that folate‐dependent de novo thymine (dTMP) biosynthesis takes place in the nucleus at the sites of DNA replication. Enzymes involved include serine hydroxymethyl‐transferase (SHMT1 and SHMT2α), thymidylate synthase (TYMS), dihydrofolate reductase (DHFR), and C1‐tetrahydrofolate (C1‐THF) synthase. Both C1‐THF synthase and SHMT generate 5,10‐methyleneTHF, the co‐factor required for the TYMS‐catalyzed conversion of dUMP to dTMP. Pull‐down experiments with C1‐THF synthase and SHMT will confirm the hypothesis that the dTMP biosynthesis multi‐enzyme complex includes folate‐dependent C1‐THF synthase, TYMS, DHFR, and Lamin B and A/C and affects nuclear folate levels and dTMP synthesis capacity. We anticipate that C1‐THF synthase will interact with SHMT1, TYMS, DHFR and lamin proteins, since it was identified as an interacting partner in a proteomics screen. If these interactions change as a result of SHMT1 knockdown, then that will help to show that SHMT is a scaffold protein in the replication complex. These studies were supported by NIH R37DK58144 to PJS.