Flavin-dependent thymidylate synthase ThyX activity: implications for the folate cycle in bacteria.

Journal Article (Journal Article)

Although flavin-dependent ThyX proteins show thymidylate synthase activity in vitro and functionally complement thyA defects in heterologous systems, direct proof of their cellular functions is missing. Using insertional mutagenesis of Rhodobacter capsulatus thyX, we constructed the first defined thyX inactivation mutant. Phenotypic analyses of the obtained mutant strain confirmed that R. capsulatus ThyX is required for de novo thymidylate synthesis. Full complementation of the R. capsulatus thyX::spec strain to thymidine prototrophy required not only the canonical thymidylate synthase ThyA but also the dihydrofolate reductase FolA. Strikingly, we also found that addition of exogenous methylenetetrahydrofolate transiently inhibited the growth of the different Rhodobacter strains used in this work. To rationalize these experimental results, we used a mathematical model of bacterial folate metabolism. This model suggests that a very low dihydrofolate reductase activity is enough to rescue significant thymidylate synthesis in the presence of ThyX proteins and is in agreement with the notion that intracellular accumulation of folates results in growth inhibition. In addition, our observations suggest that the presence of flavin-dependent thymidylate synthase X provides growth benefits under conditions in which the level of reduced folate derivatives is compromised.

Full Text

Duke Authors

Cited Authors

  • Leduc, D; Escartin, F; Nijhout, HF; Reed, MC; Liebl, U; Skouloubris, S; Myllykallio, H

Published Date

  • December 2007

Published In

Volume / Issue

  • 189 / 23

Start / End Page

  • 8537 - 8545

PubMed ID

  • 17890305

Pubmed Central ID

  • PMC2168944

Electronic International Standard Serial Number (EISSN)

  • 1098-5530

International Standard Serial Number (ISSN)

  • 0021-9193

Digital Object Identifier (DOI)

  • 10.1128/jb.01380-07


  • eng