The thiamine biosynthetic enzyme ThiC catalyzes multiple turnovers and is inhibited by S-adenosylmethionine (AdoMet) metabolites

J Biol Chem. 2013 Oct 18;288(42):30693-30699. doi: 10.1074/jbc.M113.500280. Epub 2013 Sep 6.


ThiC (4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate synthase; EC is a radical S-adenosylmethionine (AdoMet) enzyme that uses a [4Fe-4S](+) cluster to reductively cleave AdoMet to methionine and a 5'-deoxyadenosyl radical that initiates catalysis. In plants and bacteria, ThiC converts the purine intermediate 5-aminoimidazole ribotide to 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate, an intermediate of thiamine pyrophosphate (coenzyme B1) biosynthesis. In this study, assay conditions were implemented that consistently generated 5-fold molar excess of HMP, demonstrating that ThiC undergoes multiple turnovers. ThiC activity was improved by in situ removal of product 5'-deoxyadenosine. The activity was inhibited by AdoMet metabolites S-adenosylhomocysteine, adenosine, 5'-deoxyadenosine, S-methyl-5'-thioadenosine, methionine, and homocysteine. Neither adenosine nor S-methyl-5'-thioadenosine had been shown to inhibit radical AdoMet enzymes, suggesting that ThiC is distinct from other family members. The parameters for improved ThiC activity and turnover described here will facilitate kinetic and mechanistic analyses of ThiC.

Keywords: Enzyme Inhibitors; Iron-Sulfur Protein; Radicals; S-adenosylmethionine (AdoMet); Thiamine; Thiamine Biosynthesis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Catalysis
  • Kinetics
  • S-Adenosylmethionine / chemistry
  • S-Adenosylmethionine / genetics
  • S-Adenosylmethionine / metabolism*
  • Thiamine Pyrophosphate / chemistry
  • Thiamine Pyrophosphate / genetics
  • Thiamine Pyrophosphate / metabolism*
  • Treponema denticola / chemistry
  • Treponema denticola / genetics
  • Treponema denticola / metabolism*


  • Bacterial Proteins
  • ThiC protein, Bacteria
  • S-Adenosylmethionine
  • Thiamine Pyrophosphate