Structural analyses of a purine biosynthetic enzyme from Mycobacterium tuberculosis reveal a novel bound nucleotide

J Biol Chem. 2011 Nov 25;286(47):40706-16. doi: 10.1074/jbc.M111.291138. Epub 2011 Sep 28.


Enzymes of the de novo purine biosynthetic pathway have been identified as essential for the growth and survival of Mycobacterium tuberculosis and thus have potential for the development of anti-tuberculosis drugs. The final two steps of this pathway are carried out by the bifunctional enzyme 5-aminoimidazole-4-carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase (ATIC), also known as PurH. This enzyme has already been the target of anti-cancer drug development. We have determined the crystal structures of the M. tuberculosis ATIC (Rv0957) both with and without the substrate 5-aminoimidazole-4-carboxamide ribonucleotide, at resolutions of 2.5 and 2.2 Å, respectively. As for other ATIC enzymes, the protein is folded into two domains, the N-terminal domain (residues 1-212) containing the cyclohydrolase active site and the C-terminal domain (residues 222-523) containing the formyltransferase active site. An adventitiously bound nucleotide was found in the cyclohydrolase active site in both structures and was identified by NMR and mass spectral analysis as a novel 5-formyl derivative of an earlier intermediate in the biosynthetic pathway 4-carboxy-5-aminoimidazole ribonucleotide. This result and other studies suggest that this novel nucleotide is a cyclohydrolase inhibitor. The dimer formed by M. tuberculosis ATIC is different from those seen for human and avian ATICs, but it has a similar ∼50-Å separation of the two active sites of the bifunctional enzyme. Evidence in M. tuberculosis ATIC for reactivity of half-the-sites in the cyclohydrolase domains can be attributed to ligand-induced movements that propagate across the dimer interface and may be a common feature of ATIC enzymes.

Publication types

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

MeSH terms

  • Aminoimidazole Carboxamide / analogs & derivatives
  • Aminoimidazole Carboxamide / metabolism
  • Animals
  • Catalytic Domain
  • Crystallography, X-Ray
  • Humans
  • Hydroxymethyl and Formyl Transferases / chemistry*
  • Hydroxymethyl and Formyl Transferases / metabolism*
  • Ligands
  • Models, Molecular
  • Multienzyme Complexes / chemistry*
  • Multienzyme Complexes / metabolism*
  • Mycobacterium tuberculosis / enzymology*
  • Mycobacterium tuberculosis / metabolism
  • Nucleotide Deaminases / chemistry*
  • Nucleotide Deaminases / metabolism*
  • Protein Multimerization
  • Purine Nucleotides / biosynthesis*
  • Purine Nucleotides / metabolism*
  • Ribonucleotides / metabolism


  • Ligands
  • Multienzyme Complexes
  • Purine Nucleotides
  • Ribonucleotides
  • inosine monophosphate synthase
  • Aminoimidazole Carboxamide
  • Hydroxymethyl and Formyl Transferases
  • Nucleotide Deaminases
  • AICA ribonucleotide

Associated data

  • PDB/3ZZM
  • PDB/4A1O