2ntm
Crystal structure of PurO from Methanothermobacter thermoautotrophicus
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OverviewOverview
Inosine 5'-monophosphate (IMP) cyclohydrolase catalyzes the cyclization of, 5-formaminoimidazole-4-carboxamide ribonucleotide (FAICAR) to IMP in the, final step of de novo purine biosynthesis. Two major types of this enzyme, have been discovered to date: PurH in Bacteria and Eukarya and PurO in, Archaea. The structure of the MTH1020 gene product from, Methanothermobacter thermoautotrophicus was previously solved without, functional annotation but shows high amino acid sequence similarity to, other PurOs. We determined the crystal structure of the MTH1020 gene, product in complex with either IMP or 5-aminoimidazole-4-carboxamide, ribonucleotide (AICAR) at 2.0 and 2.6 A resolution, respectively. On the, basis of the sequence analysis, ligand-bound structures, and biochemical, data, MTH1020 is confirmed as an archaeal IMP cyclohydrolase, thus, designated as MthPurO. MthPurO has a four-layered alphabetabetaalpha core, structure, showing an N-terminal nucleophile (NTN) hydrolase fold. The, active site is located at the deep pocket between two central beta-sheets, and contains residues strictly conserved within PurOs. Comparisons of the, two types of IMP cyclohydrolase, PurO and PurH, revealed that there are no, similarities in sequence, structure, or the active site architecture, suggesting that they are evolutionarily not related to each other. The, MjR31K mutant of PurO from Methanocaldococcus jannaschii showed 76%, decreased activity and the MjE102Q mutation completely abolished enzymatic, activity, suggesting that these highly conserved residues play critical, roles in catalysis. Interestingly, green fluorescent protein (GFP), which, has no structural homology to either PurO or PurH but catalyzes a similar, intramolecular cyclohydrolase reaction required for chromophore, maturation, utilizes Arg96 and Glu222 in a mechanism analogous to that of, PurO.
About this StructureAbout this Structure
2NTM is a Single protein structure of sequence from Methanothermobacter thermautotrophicus. Active as IMP cyclohydrolase, with EC number 3.5.4.10 Full crystallographic information is available from OCA.
ReferenceReference
A novel function for the N-terminal nucleophile hydrolase fold demonstrated by the structure of an archaeal inosine monophosphate cyclohydrolase(,)., Kang YN, Tran A, White RH, Ealick SE, Biochemistry. 2007 May 1;46(17):5050-62. Epub 2007 Apr 4. PMID:17407260
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