title: Structural analyses of a purine biosynthetic enzyme from Mycobacterium tuberculosis reveal a novel bound nucleotide.
abstract: 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.
authors.affiliation: Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Le Nours
authors.forename: Esther M M
authors.initials: EM
authors.lastname: Bulloch
authors.forename: Zhening
authors.initials: Z
authors.lastname: Zhang
authors.forename: David R
authors.initials: DR
authors.lastname: Greenwood
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Middleditch
authors.forename: James M J
authors.initials: JM
authors.lastname: Dickson
authors.forename: Edward N
authors.initials: EN
authors.lastname: Baker
mesh_terms: D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006801:Humans; D019877:Hydroxymethyl and Formyl Transferases / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism*; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000378:metabolism; D009709:Nucleotide Deaminases / Q000737:chemistry* / Q000378:metabolism*; D055503:Protein Multimerization; D011685:Purine Nucleotides / Q000096:biosynthesis* / Q000378:metabolism*; D012265:Ribonucleotides / Q000378:metabolism
chemical_list: D008024:Ligands; D009097:Multienzyme Complexes; D011685:Purine Nucleotides; D012265:Ribonucleotides; C113120:inosine monophosphate synthase; D000620:Aminoimidazole Carboxamide; D019877:Hydroxymethyl and Formyl Transferases; D009709:Nucleotide Deaminases; C031143:AICA ribonucleotide