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Burgis NE, VanWormer K, Robbins D, Smith J. An ITPA Enzyme with Improved Substrate Selectivity. Protein J 2024; 43:62-71. [PMID: 38066288 PMCID: PMC10901923 DOI: 10.1007/s10930-023-10162-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/03/2023] [Indexed: 02/29/2024]
Abstract
Recent clinical data have identified infant patients with lethal ITPA deficiencies. ITPA is known to modulate ITP concentrations in cells and has a critical function in neural development which is not understood. Polymorphism of the ITPA gene affects outcomes for both ribavirin and thiopurine based therapies and nearly one third of the human population is thought to harbor ITPA polymorphism. In a previous site-directed mutagenesis alanine screen of the ITPA substrate selectivity pocket, we identified the ITPA mutant, E22A, as a gain-of function mutant with enhanced ITP hydrolysis activity. Here we report a rational enzyme engineering experiment to investigate the biochemical properties of position 22 ITPA mutants and find that the E22D ITPA has two- and four-fold improved substrate selectivity for ITP over the canonical purine triphosphates ATP and GTP, respectively, while maintaining biological activity. The novel E22D ITPA should be considered as a platform for further development of ITPA therapies.
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Affiliation(s)
- Nicholas E Burgis
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA.
| | - Kandise VanWormer
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA
| | - Devin Robbins
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA
| | - Jonathan Smith
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA
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2
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Mahillon M, Brodard J, Dubuis N, Gugerli P, Blouin AG, Schumpp O. Mixed infection of ITPase-encoding potyvirid and secovirid in Mercurialis perennis: evidences for a convergent euphorbia-specific viral counterstrike. Virol J 2024; 21:6. [PMID: 38178191 PMCID: PMC10768138 DOI: 10.1186/s12985-023-02257-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 12/04/2023] [Indexed: 01/06/2024] Open
Abstract
BACKGROUND In cellular organisms, inosine triphosphate pyrophosphatases (ITPases) prevent the incorporation of mutagenic deaminated purines into nucleic acids. These enzymes have also been detected in the genomes of several plant RNA viruses infecting two euphorbia species. In particular, two ipomoviruses produce replicase-associated ITPases to cope with high concentration of non-canonical nucleotides found in cassava tissues. METHOD Using high-throughput RNA sequencing on the wild euphorbia species Mercurialis perennis, two new members of the families Potyviridae and Secoviridae were identified. Both viruses encode for a putative ITPase, and were found in mixed infection with a new partitivirid. Following biological and genomic characterization of these viruses, the origin and function of the phytoviral ITPases were investigated. RESULTS While the potyvirid was shown to be pathogenic, the secovirid and partitivirid could not be transmitted. The secovirid was found belonging to a proposed new Comovirinae genus tentatively named "Mercomovirus", which also accommodates other viruses identified through transcriptome mining, and for which an asymptomatic pollen-associated lifestyle is suspected. Homology and phylogenetic analyses inferred that the ITPases encoded by the potyvirid and secovirid were likely acquired through independent horizontal gene transfer events, forming lineages distinct from the enzymes found in cassava ipomoviruses. Possible origins from cellular organisms are discussed for these proteins. In parallel, the endogenous ITPase of M. perennis was predicted to encode for a C-terminal nuclear localization signal, which appears to be conserved among the ITPases of euphorbias but absent in other plant families. This subcellular localization is in line with the idea that nucleic acids remain protected in the nucleus, while deaminated nucleotides accumulate in the cytoplasm where they act as antiviral molecules. CONCLUSION Three new RNA viruses infecting M. perennis are described, two of which encoding for ITPases. These enzymes have distinct origins, and are likely required by viruses to circumvent high level of cytoplasmic non-canonical nucleotides. This putative plant defense mechanism has emerged early in the evolution of euphorbias, and seems to specifically target certain groups of RNA viruses infecting perennial hosts.
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Affiliation(s)
- Mathieu Mahillon
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland
| | - Justine Brodard
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland
| | - Nathalie Dubuis
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland
| | - Paul Gugerli
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland
| | - Arnaud G Blouin
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland
| | - Olivier Schumpp
- Research Group Virology, Bacteriology and Phytoplasmology, Plant Protection Department, Agroscope, Nyon, Switzerland.
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3
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Broderick K, Moutaoufik MT, Aly KA, Babu M. Sanitation enzymes: Exquisite surveillance of the noncanonical nucleotide pool to safeguard the genetic blueprint. Semin Cancer Biol 2023; 94:11-20. [PMID: 37211293 DOI: 10.1016/j.semcancer.2023.05.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 05/14/2023] [Accepted: 05/17/2023] [Indexed: 05/23/2023]
Abstract
Reactive oxygen species (ROS) are common products of normal cellular metabolism, but their elevated levels can result in nucleotide modifications. These modified or noncanonical nucleotides often integrate into nascent DNA during replication, causing lesions that trigger DNA repair mechanisms such as the mismatch repair machinery and base excision repair. Four superfamilies of sanitization enzymes can effectively hydrolyze noncanonical nucleotides from the precursor pool and eliminate their unintended incorporation into DNA. Notably, we focus on the representative MTH1 NUDIX hydrolase, whose enzymatic activity is ostensibly nonessential under normal physiological conditions. Yet, the sanitization attributes of MTH1 are more prevalent when ROS levels are abnormally high in cancer cells, rendering MTH1 an interesting target for developing anticancer treatments. We discuss multiple MTH1 inhibitory strategies that have emerged in recent years, and the potential of NUDIX hydrolases as plausible targets for the development of anticancer therapeutics.
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Affiliation(s)
- Kirsten Broderick
- Department of Biochemistry, University of Regina, Regina, Saskatchewan, Canada
| | | | - Khaled A Aly
- Department of Biochemistry, University of Regina, Regina, Saskatchewan, Canada
| | - Mohan Babu
- Department of Biochemistry, University of Regina, Regina, Saskatchewan, Canada.
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4
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Burgis NE, April C, VanWormer K. Arginine-178 is an essential residue for ITPA function. Arch Biochem Biophys 2023; 744:109700. [PMID: 37506994 PMCID: PMC10530447 DOI: 10.1016/j.abb.2023.109700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Revised: 07/18/2023] [Accepted: 07/22/2023] [Indexed: 07/30/2023]
Abstract
The inosine triphosphate pyrophosphatase (ITPA) enzyme plays a critical cellular role by removing noncanonical nucleoside triphosphates from nucleotide pools. One of the first pathological ITPA mutants identified is R178C (rs746930990), which causes a fatal infantile encephalopathy, termed developmental and epileptic encephalopathy 35 (DEE 35). The accumulation of noncanonical nucleotides such as inosine triphosphate (ITP), is suspected to affect RNA and/or interfere with normal nucleotide function, leading to development of DEE 35. Molecular dynamics simulations have shown that the very rare R178C mutation does not significantly perturb the overall structure of the protein, but results in a high level of structural flexibility and disrupts active-site hydrogen bond networks, while preliminary biochemical data indicate that ITP hydrolyzing activity is significantly reduced for the R178C mutant. Here we report Michaelis-Menten enzyme kinetics data for the R178C ITPA mutant and three other position 178 ITPA mutants. These data confirm that position 178 is essential for ITPA activity and even conservative mutation at this site (R178K) results in significantly reduced enzyme activity. Our data support that disruption of the active-site hydrogen bond network is a major cause of diminished ITP hydrolyzing activity for the R178C mutation. These results suggest an avenue for developing therapies to address DEE 35.
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Affiliation(s)
- Nicholas E Burgis
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA.
| | - Caitlin April
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA
| | - Kandise VanWormer
- Department of Chemistry, Biochemistry & Physics, Eastern Washington University, Cheney, WA, 99004, USA
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5
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Straube H, Straube J, Rinne J, Fischer L, Niehaus M, Witte CP, Herde M. An inosine triphosphate pyrophosphatase safeguards plant nucleic acids from aberrant purine nucleotides. THE NEW PHYTOLOGIST 2023; 237:1759-1775. [PMID: 36464781 DOI: 10.1111/nph.18656] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 11/22/2022] [Indexed: 06/17/2023]
Abstract
In plants, inosine is enzymatically introduced in some tRNAs, but not in other RNAs or DNA. Nonetheless, our data show that RNA and DNA from Arabidopsis thaliana contain (deoxy)inosine, probably derived from nonenzymatic adenosine deamination in nucleic acids and usage of (deoxy)inosine triphosphate (dITP and ITP) during nucleic acid synthesis. We combined biochemical approaches, LC-MS, as well as RNA-Seq to characterize a plant INOSINE TRIPHOSPHATE PYROPHOSPHATASE (ITPA) from A. thaliana, which is conserved in many organisms, and investigated the sources of deaminated purine nucleotides in plants. Inosine triphosphate pyrophosphatase dephosphorylates deaminated nucleoside di- and triphosphates to the respective monophosphates. ITPA loss-of-function causes inosine di- and triphosphate accumulation in vivo and an elevated inosine and deoxyinosine content in RNA and DNA, respectively, as well as salicylic acid (SA) accumulation, early senescence, and upregulation of transcripts associated with immunity and senescence. Cadmium-induced oxidative stress and biochemical inhibition of the INOSINE MONOPHOSPHATE DEHYDROGENASE leads to more IDP and ITP in the wild-type (WT), and this effect is enhanced in itpa mutants, suggesting that ITP originates from ATP deamination and IMP phosphorylation. Inosine triphosphate pyrophosphatase is part of a molecular protection system in plants, preventing the accumulation of (d)ITP and its usage for nucleic acid synthesis.
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Affiliation(s)
- Henryk Straube
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Jannis Straube
- Department of Molecular Plant Breeding, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Jannis Rinne
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Lisa Fischer
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Markus Niehaus
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Claus-Peter Witte
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
| | - Marco Herde
- Department of Molecular Nutrition and Biochemistry of Plants, Leibniz Universität Hannover, Hannover, 30419, Germany
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Inosine triphosphate pyrophosphatase from Trypanosoma brucei cleanses cytosolic pools from deaminated nucleotides. Sci Rep 2022; 12:6408. [PMID: 35436992 PMCID: PMC9016069 DOI: 10.1038/s41598-022-10149-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 04/04/2022] [Indexed: 11/09/2022] Open
Abstract
AbstractInosine triphosphate pyrophosphatases (ITPases) are ubiquitous house-cleaning enzymes that specifically recognize deaminated purine nucleotides and catalyze their hydrolytic cleavage. In this work, we have characterized the Trypanosoma brucei ITPase ortholog (TbITPA). Recombinant TbITPA efficiently hydrolyzes (deoxy)ITP and XTP nucleotides into their respective monophosphate form. Immunolocalization analysis performed in bloodstream forms suggests that the primary role of TbITPA is the exclusion of deaminated purines from the cytosolic nucleoside triphosphate pools. Even though ITPA-knockout bloodstream parasites are viable, they are more sensitive to inhibition of IMP dehydrogenase with mycophenolic acid, likely due to an expansion of IMP, the ITP precursor. On the other hand, TbITPA can also hydrolyze the activated form of the antiviral ribavirin although in this case, the absence of ITPase activity in the cell confers protection against this nucleoside analog. This unexpected phenotype is dependant on purine availability and can be explained by the fact that ribavirin monophosphate, the reaction product generated by TbITPA, is a potent inhibitor of trypanosomal IMP dehydrogenase and GMP reductase. In summary, the present study constitutes the first report on a protozoan inosine triphosphate pyrophosphatase involved in the removal of harmful deaminated nucleotides from the cytosolic pool.
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Association of ITPA gene polymorphisms with adverse effects of AZA/6-MP administration: a systematic review and meta-analysis. THE PHARMACOGENOMICS JOURNAL 2022; 22:39-54. [PMID: 35034963 DOI: 10.1038/s41397-021-00255-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 08/24/2021] [Accepted: 09/20/2021] [Indexed: 02/07/2023]
Abstract
Azathioprine (AZA) and its metabolite, mercaptopurine (6-MP), are widely used immunosuppressant drugs. Polymorphisms in genes implicated in AZA/6-MP metabolism, reportedly, could account in part for their potential toxicity. In the present study we performed a systematic review and a meta-analysis, comprising 30 studies and 3582 individuals, to investigate the putative genetic association of two inosine triphosphatase (ITPA) polymorphisms with adverse effects in patients treated with AZA/6-MP. We found that rs1127354 is associated with neutropenia in general populations and in children (OR: 2.39, 95%CI: 1.97-2.90, and OR: 2.43, 95%CI: 2.12-2.79, respectively), and with all adverse effects tested herein in adult populations (OR: 2.12, 95%CI: 1.22-3.69). We also found that rs7270101 is associated with neutropenia and leucopenia in all-ages populations (OR: 2.93, 95%CI: 2.36-3.63, and OR: 2.82, 95%CI: 1.76-4.50, respectively) and with all adverse effects tested herein in children (OR: 1.74, 95%CI: 1.06-2.87). Stratification according to background disease, in combination with multiple comparisons corrections, verified neutropenia to be associated with both polymorphisms, in acute lymphoblastic leukemia (ALL) patients. These findings suggest that ITPA polymorphisms could be used as predictive biomarkers for adverse effects of thiopurine drugs to eliminate intolerance in ALL patients and clarify dosing in patients with different ITPA variants.
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8
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Valli AA, García López R, Ribaya M, Martínez FJ, Gómez DG, García B, Gonzalo I, Gonzalez de Prádena A, Pasin F, Montanuy I, Rodríguez-Gonzalo E, García JA. Maf/ham1-like pyrophosphatases of non-canonical nucleotides are host-specific partners of viral RNA-dependent RNA polymerases. PLoS Pathog 2022; 18:e1010332. [PMID: 35180277 PMCID: PMC8893687 DOI: 10.1371/journal.ppat.1010332] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2021] [Revised: 03/03/2022] [Accepted: 02/02/2022] [Indexed: 11/18/2022] Open
Abstract
Cassava brown streak disease (CBSD), dubbed the “Ebola of plants”, is a serious threat to food security in Africa caused by two viruses of the family Potyviridae: cassava brown streak virus (CBSV) and Ugandan (U)CBSV. Intriguingly, U/CBSV, along with another member of this family and one secoviridae, are the only known RNA viruses encoding a protein of the Maf/ham1-like family, a group of widespread pyrophosphatase of non-canonical nucleotides (ITPase) expressed by all living organisms. Despite the socio-economic impact of CDSD, the relevance and role of this atypical viral factor has not been yet established. Here, using an infectious cDNA clone and reverse genetics, we demonstrate that UCBSV requires the ITPase activity for infectivity in cassava, but not in the model plant Nicotiana benthamiana. HPLC-MS/MS experiments showed that, quite likely, this host-specific constraint is due to an unexpected high concentration of non-canonical nucleotides in cassava. Finally, protein analyses and experimental evolution of mutant viruses indicated that keeping a fraction of the yielded UCBSV ITPase covalently bound to the viral RNA-dependent RNA polymerase (RdRP) optimizes viral fitness, and this seems to be a feature shared by the other members of the Potyviridae family expressing Maf/ham1-like proteins. All in all, our work (i) reveals that the over-accumulation of non-canonical nucleotides in the host might have a key role in antiviral defense, and (ii) provides the first example of an RdRP-ITPase partnership, reinforcing the idea that RNA viruses are incredibly versatile at adaptation to different host setups. Cassava is one the most important staple food around the world in term of caloric intake. The cassava brown streak disease, caused by cassava brown streak virus (CBSV) and Ugandan (U)CBSV–Ipomovirus genus, Potyviridae family-, produces massive losses in cassava production. Curiously, these two viruses, unlike the vast majority of members of the family, encode a Maf1/ham1-like pyrophosphatase (HAM1) of non-canonical nucleotides with unknown relevance and function in viruses. This study aims to fill this gap in our knowledge by using reverse genetics, biochemistry, metabolomics and directed virus evolution. Hence, we found that HAM1 is required for UCBSV to infect cassava, where its pyrophosphatase activity resulted critical, but not to propagate in the model plant Nicotiana benthamiana. In addition, we demonstrated that HAM1 works in partnership with the viral RdRP during infection. Unexpected high levels of ITP/XTP non-canonical nucleotides found in cassava, and the known flexibility of RNA viruses to incorporate additional factors when required, supports the idea that the high concentration of ITP/XTP worked as a selection pressure to promote the acquisition of HAM1 into the virus in order to promote a successful infection.
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Affiliation(s)
- Adrian A. Valli
- Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
- * E-mail:
| | | | - María Ribaya
- Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
| | | | - Diego García Gómez
- Departamento de Química Analítica, Nutrición y Bromatología, Universidad de Salamanca, Salamanca, Spain
| | - Beatriz García
- Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
| | - Irene Gonzalo
- Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
| | | | - Fabio Pasin
- Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
| | - Inmaculada Montanuy
- Facultad de Ciencias Experimentales, Universidad Francisco de Vitoria, Madrid, Spain
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9
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Zamzami MA. Inosine Triphosphate Pyrophosphatase (ITPase): Functions, Mutations, Polymorphisms and Its Impact on Cancer Therapies. Cells 2022; 11:384. [PMID: 35159194 PMCID: PMC8833965 DOI: 10.3390/cells11030384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 01/18/2022] [Accepted: 01/19/2022] [Indexed: 11/16/2022] Open
Abstract
Inosine triphosphate pyrophosphatase (ITPase) is an enzyme encoded by the ITPA gene and functions to prevent the incorporation of noncanonical purine nucleotides into DNA and RNA. Specifically, the ITPase catalyzed the hydrolysis of (deoxy) nucleoside triphosphates ((d) NTPs) into the corresponding nucleoside monophosphate with the concomitant release of pyrophosphate. Recently, thiopurine drug metabolites such as azathioprine have been included in the lists of ITPase substrates. Interestingly, inosine or xanthosine triphosphate (ITP/XTP) and their deoxy analogs, deoxy inosine or xanthosine triphosphate (dITP/dXTP), are products of important biological reactions such as deamination that take place within the cellular compartments. However, the incorporation of ITP/XTP, dITP/dXTP, or the genetic deficiency or polymorphism of the ITPA gene have been implicated in many human diseases, including infantile epileptic encephalopathy, early onset of tuberculosis, and the responsiveness of patients to cancer therapy. This review provides an up-to-date report on the ITPase enzyme, including information regarding its discovery, analysis, and cellular localization, its implication in human diseases including cancer, and its therapeutic potential, amongst others.
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Affiliation(s)
- Mazin A. Zamzami
- Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
- Centre of Artificial Intelligence in Precision Medicines, King Abdulaziz University, Jeddah 21589, Saudi Arabia
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10
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James AM, Seal SE, Bailey AM, Foster GD. Viral inosine triphosphatase: A mysterious enzyme with typical activity, but an atypical function. MOLECULAR PLANT PATHOLOGY 2021; 22:382-389. [PMID: 33471956 PMCID: PMC7865087 DOI: 10.1111/mpp.13021] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 10/22/2020] [Accepted: 10/23/2020] [Indexed: 05/03/2023]
Abstract
Plant viruses typically have highly condensed genomes, yet the plant-pathogenic viruses Cassava brown streak virus, Ugandan cassava brown streak virus, and Euphorbia ringspot virus are unusual in encoding an enzyme not yet found in any other virus, the "house-cleaning" enzyme inosine triphosphatase. Inosine triphosphatases (ITPases) are highly conserved enzymes that occur in all kingdoms of life and perform a house-cleaning function by hydrolysing the noncanonical nucleotide inosine triphosphate to inosine monophosphate. The ITPases encoded by cassava brown streak virus and Ugandan cassava brown streak virus have been characterized biochemically and are shown to have typical ITPase activity. However, their biological role in virus infection has yet to be elucidated. Here we review what is known of viral-encoded ITPases and speculate on potential roles in infection with the aim of generating a greater understanding of cassava brown streak viruses, a group of the world's most devastating viruses.
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Affiliation(s)
- Amy M. James
- School of Biological SciencesLife Sciences BuildingUniversity of BristolBristolUK
| | - Susan E. Seal
- Natural Resources Institute, Chatham MaritimeGillinghamUK
| | - Andy M. Bailey
- School of Biological SciencesLife Sciences BuildingUniversity of BristolBristolUK
| | - Gary D. Foster
- School of Biological SciencesLife Sciences BuildingUniversity of BristolBristolUK
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11
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Sakamoto M, Kouhei D, Haniffa M, Silva S, Troncoso M, Santander P, Schonstedt V, Stecher X, Okamoto N, Hamanaka K, Mizuguchi T, Mitsuhashi S, Miyake N, Matsumoto N. A novel ITPA variant causes epileptic encephalopathy with multiple-organ dysfunction. J Hum Genet 2020; 65:751-757. [PMID: 32405030 DOI: 10.1038/s10038-020-0765-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 03/18/2020] [Accepted: 04/13/2020] [Indexed: 11/09/2022]
Abstract
Inborn errors of metabolism can cause epileptic encephalopathies. Biallelic loss-of-function variants in the ITPA gene, encoding inosine triphosphate pyrophosphatase (ITPase), have been reported in epileptic encephalopathies with lack of myelination of the posterior limb of the internal capsule, brainstem tracts, and tracts to the primary visual and motor cortices (MIM:616647). ITPase plays an important role in purine metabolism. In this study, we identified two novel homozygous ITPA variants, c.264-1 G > A and c.489-1 G > A, in two unrelated consanguineous families. The probands had epilepsy, microcephaly with characteristic magnetic resonance imaging findings (T2 hyperintensity signals in the pyramidal tracts of the internal capsule, delayed myelination, and thin corpus callosum), hypotonia, and developmental delay; both died in early infancy. Our report expands the knowledge of clinical consequences of biallelic ITPA variants.
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Affiliation(s)
- Masamune Sakamoto
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.,Department of Pediatrics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Den Kouhei
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Muzhirah Haniffa
- Department of Genetics, Hospital Kuala Lumpur, Jalan Pahang, Malaysia
| | - Sebastián Silva
- Child Neurology Service, Hospital de Puerto Montt, Puerto Montt, Chile
| | - Mónica Troncoso
- Child Neurology Service, Hospital San Borja Arriarán, Universidad de Chile, Santiago, Chile
| | - Paola Santander
- Child Neurology Service, Hospital San Borja Arriarán, Universidad de Chile, Santiago, Chile
| | | | - Ximena Stecher
- Department of Radiology, Clínica Alemana de Santiago, Santiago, Chile.,Department of Radiology, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago, Chile
| | | | - Kohei Hamanaka
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Takeshi Mizuguchi
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Satomi Mitsuhashi
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Noriko Miyake
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.
| | - Naomichi Matsumoto
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.
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12
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Houndonougbo Y, Pugh B, VanWormer K, April C, Burgis N. Structural dynamics of inosine triphosphate pyrophosphatase (ITPA) protein and two clinically relevant mutants: molecular dynamics simulations. J Biomol Struct Dyn 2020; 39:1236-1247. [PMID: 32129147 DOI: 10.1080/07391102.2020.1727363] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The inosine triphosphate pyrophosphatase (ITPA) protein is responsible for removing noncanonical purine nucleoside triphosphates from intracellular nucleotide pools. Absence of ITPA results in genomic instability and increased levels of inosine in DNA and RNA. The proline to threonine substitution at position 32 (P32T) affects roughly 15% of the global population and can modulate treatment outcomes for cancer, lupus, and hepatitis C patients. The substitution of arginine with cysteine at position 178 (R178C) is extremely uncommon and has only been reported in a small cohort of early infantile encephalopathy patients suggesting that a functional ITPA protein is required for life in humans. Here we present molecular dynamic simulations that describe the structure and dynamics of the wild-type ITPA homodimer and two of its clinically relevant mutants, P32T and R178C. The simulation results indicate that both the P32T and R178C mutations alter the structure and dynamic properties of the protein and provide a possible explanation of the experimentally observed effect of the mutations on ITPA activity. Specifically, the mutations increased the overall flexibility of the protein and changed the dominant collective motions of the top lobe as well as the helix 2 of the lower lobe. Moreover, we have identified key active-site residues that are classified as essential or intermediate for inosine triphosphate (ITP) hydrolyzing activity based on their hydrogen bond occupancy. Here we also present biochemical data indicating that the R178C mutant has very low ITP hydrolyzing activity.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Yao Houndonougbo
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA, USA
| | - Bethany Pugh
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA, USA
| | - Kandise VanWormer
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA, USA
| | - Caitlin April
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA, USA
| | - Nicholas Burgis
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA, USA
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13
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Tomlinson KR, Pablo‐Rodriguez JL, Bunawan H, Nanyiti S, Green P, Miller J, Alicai T, Seal SE, Bailey AM, Foster GD. Cassava brown streak virus Ham1 protein hydrolyses mutagenic nucleotides and is a necrosis determinant. MOLECULAR PLANT PATHOLOGY 2019; 20:1080-1092. [PMID: 31154674 PMCID: PMC6640186 DOI: 10.1111/mpp.12813] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Cassava brown streak disease (CBSD) is a leading cause of cassava losses in East and Central Africa, and is currently having a severe impact on food security. The disease is caused by two viruses within the Potyviridae family: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), which both encode atypical Ham1 proteins with highly conserved inosine triphosphate (ITP) pyrophosphohydrolase (ITPase) domains. ITPase proteins are widely encoded by plant, animal, and archaea. They selectively hydrolyse mutagenic nucleotide triphosphates to prevent their incorporation into nucleic acid and thereby function to reduce mutation rates. It has previously been hypothesized that U/CBSVs encode Ham1 proteins with ITPase activity to reduce viral mutation rates during infection. In this study, we investigate the potential roles of U/CBSV Ham1 proteins. We show that both CBSV and UCBSV Ham1 proteins have ITPase activities through in vitro enzyme assays. Deep-sequencing experiments found no evidence of the U/CBSV Ham1 proteins providing mutagenic protection during infections of Nicotiana hosts. Manipulations of the CBSV_Tanza infectious clone were performed, including a Ham1 deletion, ITPase point mutations, and UCBSV Ham1 chimera. Unlike severely necrotic wild-type CBSV_Tanza infections, infections of Nicotiana benthamiana with the manipulated CBSV infectious clones do not develop necrosis, indicating that that the CBSV Ham1 is a necrosis determinant. We propose that the presence of U/CBSV Ham1 proteins with highly conserved ITPase motifs indicates that they serve highly selectable functions during infections of cassava and may represent a euphorbia host adaptation that could be targeted in antiviral strategies.
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Affiliation(s)
- Katie R. Tomlinson
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
| | - José Luis Pablo‐Rodriguez
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
- CINVESTAVCampus IrapuatoMexico
| | - Hamidun Bunawan
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
- Institute of Systems Biology (INBIOSIS)Universiti Kebangsaan Malaysia, UKMBangi43600Selangor Darul EhsanMalaysia
| | - Sarah Nanyiti
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
- National Crops Resources Research Institute (NaCRRI)P.O. Box 7084KampalaUganda
| | - Patrick Green
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
| | - Josie Miller
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
| | - Titus Alicai
- National Crops Resources Research Institute (NaCRRI)P.O. Box 7084KampalaUganda
| | - Susan E. Seal
- Natural Resources InstituteChatham Maritime, KentME4 4TBUK
| | - Andy M. Bailey
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
| | - Gary D. Foster
- School of Biological SciencesUniversity of BristolLife Sciences Building, 24 Tyndall Avenue BristolBS8 1TQUK
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14
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Kumar H, Kehrer J, Singer M, Reinig M, Santos JM, Mair GR, Frischknecht F. Functional genetic evaluation of DNA house-cleaning enzymes in the malaria parasite: dUTPase and Ap4AH are essential in Plasmodium berghei but ITPase and NDH are dispensable. Expert Opin Ther Targets 2019; 23:251-261. [PMID: 30700216 DOI: 10.1080/14728222.2019.1575810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Accepted: 01/25/2019] [Indexed: 02/06/2023]
Abstract
BACKGROUND Cellular metabolism generates reactive oxygen species. The oxidation and deamination of the deoxynucleoside triphosphate (dNTP) pool results in the formation of non-canonical, toxic dNTPs that can cause mutations, genome instability, and cell death. House-cleaning or sanitation enzymes that break down and detoxify non-canonical nucleotides play major protective roles in nucleotide metabolism and constitute key drug targets for cancer and various pathogens. We hypothesized that owing to their protective roles in nucleotide metabolism, these house-cleaning enzymes are key drug targets in the malaria parasite. METHODS Using the rodent malaria parasite Plasmodium berghei we evaluate here, by gene targeting, a group of conserved proteins with a putative function in the detoxification of non-canonical nucleotides as potential antimalarial drug targets: they are inosine triphosphate pyrophosphatase (ITPase), deoxyuridine triphosphate pyrophosphatase (dUTPase) and two NuDiX hydroxylases, the diadenosine tetraphosphate (Ap4A) hydrolase and the nucleoside triphosphate hydrolase (NDH). RESULTS While all four proteins are expressed constitutively across the intraerythrocytic developmental cycle, neither ITPase nor NDH are required for parasite viability. dutpase and ap4ah null mutants, on the other hand, are not viable suggesting an essential function for these proteins for the malaria parasite. CONCLUSIONS Plasmodium dUTPase and Ap4A could be drug targets in the malaria parasite.
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Affiliation(s)
- Hirdesh Kumar
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
| | - Jessica Kehrer
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
| | - Mirko Singer
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
| | - Miriam Reinig
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
| | - Jorge M Santos
- b Instituto de Medicina Molecular , Faculdade de Medicina da Universidade de Lisboa , Lisbon , Portugal
| | - Gunnar R Mair
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
- b Instituto de Medicina Molecular , Faculdade de Medicina da Universidade de Lisboa , Lisbon , Portugal
- c Department of Biomedical Sciences , 2008 College of Veterinary Medicine, Iowa State University , Ames , IA USA
| | - Friedrich Frischknecht
- a Integrative Parasitology, Department of Infectious Diseases , University of Heidelberg Medical School , Heidelberg , Germany
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15
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Kaur P, Neethukrishna K, Kumble A, Girisha KM, Shukla A. Identification of a novel homozygous variant confirms ITPA as a developmental and epileptic encephalopathy gene. Am J Med Genet A 2019; 179:857-861. [PMID: 30816001 DOI: 10.1002/ajmg.a.61103] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 01/24/2019] [Accepted: 01/26/2019] [Indexed: 11/07/2022]
Abstract
ITPA related epileptic encephalopathy (epileptic encephalopathy, early infantile, 35) is a rare inborn error of metabolism. All reported individuals with this condition, including the present case manifest global developmental delay, seizures, progressive postnatal microcephaly, hypotonia, thin corpus callosum, cerebral atrophy, delayed myelination and white matter changes in posterior limb of internal capsule. Cataract and dilated cardiomyopathy are other characteristic findings. Currently, a single publication describes this condition in four families. Three truncating and two missense variants in ITPA have been identified in these families. We hereby report another family with ITPA related disorder and review the genotype and phenotype of the reported subjects.
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Affiliation(s)
- Parneet Kaur
- Department of Medical Genetics, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, India
| | - Kausthubham Neethukrishna
- Department of Medical Genetics, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, India
| | - Ali Kumble
- Department of Paediatrics, Indiana Hospital and Heart Institute, Mangalore, India
| | - Katta M Girisha
- Department of Medical Genetics, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, India
| | - Anju Shukla
- Department of Medical Genetics, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, India
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16
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Mollaahmadi F, Moini A, Salman Yazdi R, Behmanesh M. The rs1127354 Polymorphism in ITPA Is Associated with Susceptibility to Infertility. CELL JOURNAL 2018; 20:73-77. [PMID: 29308621 PMCID: PMC5759682 DOI: 10.22074/cellj.2018.4255] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 01/21/2017] [Indexed: 12/29/2022]
Abstract
Objective Infertility is a common human disorder which is defined as the failure to conceive for a period of 12 months
without contraception. Many studies have shown that the outcome of fertility could be affected by DNA damage. We
attempted to examine the association of two SNPs (rs1127354 and rs7270101) in ITPA, a gene encoding a key factor
in the repair system, with susceptibility to infertility.
Materials and Methods This was a case-control study of individuals with established infertility. Blood samples were
obtained from 164 infertile patients and 180 ethnically matched fertile controls. Total genomic DNA were extracted
from whole blood using the standard salting out method, and stored at -20˚C. Genotyping were based on mismatch
polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in which PCR products were
digested with the XmnI restriction enzyme and run on a 12% polyacrylamide gel.
Results All genotype frequencies in the control group were in Hardy-Weinberg equilibrium. A significant association
(in allelic, recessive and dominant genotypic models) was observed between infertile patients and healthy controls
based on rs1127354 (P=0.0001), however, no significant association was detected for rs7270101. Also, gender
stratification and analysis of different genotype models did not lead to a significant association for this single-
nucleotide polymorphis (SNP).
Conclusion ITPA is likely to be a genetic determinant for decreased fertility. To the best of our knowledge, this is the
first report demonstrating this association, however, given the small sample size and other limitations, genotyping of
this SNP is recommended to be carried out in different populations with more samples.
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Affiliation(s)
- Fahimeh Mollaahmadi
- Department of Genetics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran.,Department of Endocrinology and Female Infertility, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran
| | - Ashraf Moini
- Department of Endocrinology and Female Infertility, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran
| | - Reza Salman Yazdi
- Department of Andrology, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran
| | - Mehrdad Behmanesh
- Department of Genetics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran.
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17
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Ji D, Stepchenkova EI, Cui J, Menezes MR, Pavlov YI, Kool ET. Measuring deaminated nucleotide surveillance enzyme ITPA activity with an ATP-releasing nucleotide chimera. Nucleic Acids Res 2017; 45:11515-11524. [PMID: 29036687 PMCID: PMC5714213 DOI: 10.1093/nar/gkx774] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 08/23/2017] [Indexed: 01/24/2023] Open
Abstract
Nucleotide quality surveillance enzymes play important roles in human health, by detecting damaged molecules in the nucleotide pool and deactivating them before they are incorporated into chromosomal DNA or adversely affect metabolism. In particular, deamination of adenine moiety in (deoxy)nucleoside triphosphates, resulting in formation of (d)ITP, can be deleterious, leading to DNA damage, mutagenesis and other harmful cellular effects. The 21.5 kDa human enzyme that mitigates this damage by conversion of (d)ITP to monophosphate, ITPA, has been proposed as a possible therapeutic and diagnostic target for multiple diseases. Measuring the activity of this enzyme is useful both in basic research and in clinical applications involving this pathway, but current methods are nonselective and are not applicable to measurement of the enzyme from cells or tissues. Here, we describe the design and synthesis of an ITPA-specific chimeric dinucleotide (DIAL) that replaces the pyrophosphate leaving group of the native substrate with adenosine triphosphate, enabling sensitive detection via luciferase luminescence signaling. The probe is shown to function sensitively and selectively to quantify enzyme activity in vitro, and can be used to measure the activity of ITPA in bacterial, yeast and human cell lysates.
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Affiliation(s)
- Debin Ji
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Elena I Stepchenkova
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA.,Department of Genetics and Biotechnology, Saint-Petersburg State University, St Petersburg, 199034, Russia.,Saint-Petersburg Branch of Vavilov Institute of General Genetics, RAS, St Petersburg, 199034, Russia
| | - Jian Cui
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Miriam R Menezes
- Department of Neurosurgery, University of Texas Health Science Center, Houston, TX 77030, USA
| | - Youri I Pavlov
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA.,Departments of Biochemistry and Molecular Biology; Microbiology and Pathology; Genetics Cell Biology and Anatomy; University of Nebraska Medical Center, Omaha, NE 61818, USA
| | - Eric T Kool
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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18
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Burgis NE. A disease spectrum for ITPA variation: advances in biochemical and clinical research. J Biomed Sci 2016; 23:73. [PMID: 27770805 PMCID: PMC5075207 DOI: 10.1186/s12929-016-0291-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 10/19/2016] [Indexed: 12/15/2022] Open
Abstract
Human ITPase (encoded by the ITPA gene) is a protective enzyme which acts to exclude noncanonical (deoxy)nucleoside triphosphates ((d)NTPs) such as (deoxy)inosine 5′-triphosphate ((d)ITP), from (d)NTP pools. Until the last few years, the importance of ITPase in human health and disease has been enigmatic. In 2009, an article was published demonstrating that ITPase deficiency in mice is lethal. All homozygous null offspring died before weaning as a result of cardiomyopathy due to a defect in the maintenance of quality ATP pools. More recently, a whole exome sequencing project revealed that very rare, severe human ITPA mutation results in early infantile encephalopathy and death. It has been estimated that nearly one third of the human population has an ITPA status which is associated with decreased ITPase activity. ITPA status has been linked to altered outcomes for patients undergoing thiopurine or ribavirin therapy. Thiopurine therapy can be toxic for patients with ITPA polymorphism, however, ITPA polymorphism is associated with improved outcomes for patients undergoing ribavirin treatment. ITPA polymorphism has also been linked to early-onset tuberculosis susceptibility. These data suggest a spectrum of ITPA-related disease exists in human populations. Potentially, ITPA status may affect a large number of patient outcomes, suggesting that modulation of ITPase activity is an important emerging avenue for reducing the number of negative outcomes for ITPA-related disease. Recent biochemical studies have aimed to provide rationale for clinical observations, better understand substrate selectivity and provide a platform for modulation of ITPase activity.
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Affiliation(s)
- Nicholas E Burgis
- Department of Chemistry and Biochemistry, Eastern Washington University, 226 Science Building, Cheney, WA, 99004, USA.
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19
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Kevelam SH, Bierau J, Salvarinova R, Agrawal S, Honzik T, Visser D, Weiss MM, Salomons GS, Abbink TEM, Waisfisz Q, van der Knaap MS. Recessive ITPA mutations cause an early infantile encephalopathy. Ann Neurol 2015. [PMID: 26224535 DOI: 10.1002/ana.24496] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE To identify the etiology of a novel, heritable encephalopathy in a small group of patients. METHODS Magnetic resonance imaging (MRI) pattern analysis was used to select patients with the same pattern. Homozygosity mapping and whole exome sequencing (WES) were performed to find the causal gene mutations. RESULTS Seven patients from 4 families (2 consanguineous) were identified with a similar MRI pattern characterized by T2 signal abnormalities and diffusion restriction in the posterior limb of the internal capsule, often also optic radiation, brainstem tracts, and cerebellar white matter, in combination with delayed myelination and progressive brain atrophy. Patients presented with early infantile onset encephalopathy characterized by progressive microcephaly, seizures, variable cardiac defects, and early death. Metabolic testing was unrevealing. Single nucleotide polymorphism array revealed 1 overlapping homozygous region on chromosome 20 in the consanguineous families. In all patients, WES subsequently revealed recessive predicted loss of function mutations in ITPA, encoding inosine triphosphate pyrophosphatase (ITPase). ITPase activity in patients' erythrocytes and fibroblasts was severely reduced. INTERPRETATION Until now ITPA variants have only been associated with adverse reactions to specific drugs. This is the first report associating ITPA mutations with a human disorder. ITPase is important in purine metabolism because it removes noncanonical nucleotides from the cellular nucleotide pool. Toxicity of accumulated noncanonical nucleotides, leading to neuronal apoptosis and interference with proteins normally using adenosine triphosphate/guanosine triphosphate, probably explains the disease. This study confirms that combining MRI pattern recognition to define small, homogeneous patient groups with WES is a powerful approach for providing a fast diagnosis in patients with an unclassified genetic encephalopathy.
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Affiliation(s)
- Sietske H Kevelam
- Department of Child Neurology, VU University Medical Center, Amsterdam, the Netherlands.,Neuroscience Campus Amsterdam, VU University, Amsterdam, the Netherlands
| | - Jörgen Bierau
- Department of Clinical Genetics, Maastricht University Medical Center, Maastricht, the Netherlands
| | - Ramona Salvarinova
- Division of Biochemical Diseases, Department of Pediatrics, University of British Columbia, British Columbia Children's Hospital, Vancouver, British Columbia, Canada
| | - Shakti Agrawal
- Department of Pediatric Neurology, Birmingham Children's Hospital, Birmingham, United Kingdom
| | - Tomas Honzik
- Department of Pediatrics, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Prague, Czech Republic
| | - Dennis Visser
- Department of Clinical Genetics, Maastricht University Medical Center, Maastricht, the Netherlands
| | - Marjan M Weiss
- Department of Clinical Genetics, VU University Medical Center, Amsterdam, the Netherlands
| | - Gajja S Salomons
- Neuroscience Campus Amsterdam, VU University, Amsterdam, the Netherlands.,Department of Clinical Chemistry, Metabolic Unit, VU University Medical Center, Amsterdam, the Netherlands
| | - Truus E M Abbink
- Department of Child Neurology, VU University Medical Center, Amsterdam, the Netherlands.,Neuroscience Campus Amsterdam, VU University, Amsterdam, the Netherlands
| | - Quinten Waisfisz
- Department of Clinical Genetics, VU University Medical Center, Amsterdam, the Netherlands
| | - Marjo S van der Knaap
- Department of Child Neurology, VU University Medical Center, Amsterdam, the Netherlands.,Neuroscience Campus Amsterdam, VU University, Amsterdam, the Netherlands.,Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands
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20
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Dushanov EB, Kholmurodov KT, Koltovaya NA. Simulation of mutant P32T homo- and heterodimers of human inosine triphosphate pyrophosphatase hITPA. Biophysics (Nagoya-shi) 2015. [DOI: 10.1134/s0006350915040090] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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21
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Nagy GN, Leveles I, Vértessy BG. Preventive DNA repair by sanitizing the cellular (deoxy)nucleoside triphosphate pool. FEBS J 2014; 281:4207-23. [PMID: 25052017 DOI: 10.1111/febs.12941] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2014] [Revised: 07/01/2014] [Accepted: 07/16/2014] [Indexed: 01/24/2023]
Abstract
The occurrence of modified bases in DNA is attributed to some major factors: incorporation of altered nucleotide building blocks and chemical reactions or radiation effects on bases within the DNA structure. Several enzyme families are involved in preventing the incorporation of noncanonical bases playing a 'sanitizing' role. The catalytic mechanism of action of these enzymes has been revealed for a number of representatives in clear structural and kinetic detail. In this review, we focus in detail on those examples where clear evidence has been produced using high-resolution structural studies. Comparing the protein fold and architecture of the enzyme active sites, two main classes of sanitizing deoxyribonucleoside triphosphate pyrophosphatases can be assigned that are distinguished by the site of nucleophilic attack. In enzymes associated with attack at the α-phosphorus, it is shown that coordination of the γ-phosphate group is also ensured by multiple interactions. By contrast, enzymes catalyzing attack at the β-phosphorus atom mainly coordinate the α- and the β-phosphate only. Characteristic differences are also observed with respect to the role of the metal ion cofactor (Mg(2+) ) and the coordination of nucleophilic water. Using different catalytic mechanisms embedded in different protein folds, these enzymes present a clear example of convergent evolution.
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Affiliation(s)
- Gergely N Nagy
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary; Department of Applied Biotechnology and Food Science, Budapest University of Technology and Economics, Hungary
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22
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Fujishiro T, Tamura H, Schick M, Kahnt J, Xie X, Ermler U, Shima S. Identification of the HcgB Enzyme in [Fe]-Hydrogenase-Cofactor Biosynthesis. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201306745] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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23
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Fujishiro T, Tamura H, Schick M, Kahnt J, Xie X, Ermler U, Shima S. Identification of the HcgB enzyme in [Fe]-hydrogenase-cofactor biosynthesis. Angew Chem Int Ed Engl 2013; 52:12555-8. [PMID: 24249552 DOI: 10.1002/anie.201306745] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 09/23/2013] [Indexed: 11/10/2022]
Affiliation(s)
- Takashi Fujishiro
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse 10, 35043 Marburg (Germany) http://www.mpi-marburg.mpg.de/
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24
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Gall AD, Gall A, Moore AC, Aune MK, Heid S, Mori A, Burgis NE. Analysis of human ITPase nucleobase specificity by site-directed mutagenesis. Biochimie 2013; 95:1711-21. [PMID: 23770441 DOI: 10.1016/j.biochi.2013.05.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Accepted: 05/23/2013] [Indexed: 02/07/2023]
Abstract
Inosine triphosphate (ITP) pyrophosphohydrolase, or ITPase, is an intracellular enzyme that is responsible for the hydrolysis of the acidic anhydride bond between the alpha and beta phosphates in ITP, and other noncanonical nucleoside triphosphates, producing the corresponding nucleoside monophosphate and pyrophosphate. This activity protects the cell by preventing noncanonical nucleoside triphosphates from accumulating in (deoxy) nucleoside triphosphate ((d)NTP) pools and/or being integrated into nucleic acids. This enzyme is encoded by the ITPA gene in mammals. It has been reported that Itpa homozygous-null knock-out mice die before weaning and have gross cardiac abnormalities. Additionally, certain variations in the human ITPA gene have been linked to adverse reactions to the immunosuppressive prodrugs azathioprine and 6-mercaptopurine and protection against ribavirin-induced hemolytic anemia. These drugs are bioactivated to form noncanonical nucleoside triphosphates. Human ITPase enzymes engineered to modulate nucleobase specificity may be valuable tools for studying the role of ITPase in heart development and drug metabolism or developing gain-of-function mutants or inhibitory molecules. Based on x-ray crystallography and amino acid sequence data, a panel of putative human ITPase nucleobase specificity mutants has been generated. We targeted eight highly conserved amino acid positions within the ITPase sequence that correspond to amino acids predicted to directly interact with the nucleobase or help organize the nucleobase binding pocket. The ability of the mutants to protect against exogenous and endogenous noncanonical purines was tested with two Escherichia coli complementation assays. Nucleobase specificity of the mutants was investigated with an in vitro biochemical assay using ITP, GTP and ATP as substrates. This methodology allowed us to identify gain-of-function mutants and categorize the eight amino acid positions according to their ability to protect against noncanonical purines as follows: Glu-22, Trp-151 and Arg-178, essential for protection; Phe-149, Asp-152, Lys-172 and Ser-176, intermediate protection; His-177, dispensable for protection against noncanonical purines.
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Affiliation(s)
- Amanda D Gall
- Department of Chemistry and Biochemistry, Eastern Washington University, 226 Science Building, Cheney, WA 99004, USA
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25
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Simone PD, Pavlov YI, Borgstahl GEO. ITPA (inosine triphosphate pyrophosphatase): from surveillance of nucleotide pools to human disease and pharmacogenetics. Mutat Res 2013; 753:131-146. [PMID: 23969025 DOI: 10.1016/j.mrrev.2013.08.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/31/2013] [Accepted: 08/02/2013] [Indexed: 01/08/2023]
Abstract
Cellular nucleotide pools are often contaminated by base analog nucleotides which interfere with a plethora of biological reactions, from DNA and RNA synthesis to cellular signaling. An evolutionarily conserved inosine triphosphate pyrophosphatase (ITPA) removes the non-canonical purine (d)NTPs inosine triphosphate and xanthosine triphosphate by hydrolyzing them into their monophosphate form and pyrophosphate. Mutations in the ITPA orthologs in model organisms lead to genetic instability and, in mice, to severe developmental anomalies. In humans there is genetic polymorphism in ITPA. One allele leads to a proline to threonine substitution at amino acid 32 and causes varying degrees of ITPA deficiency in tissues and plays a role in patients' response to drugs. Structural analysis of this mutant protein reveals that the protein is destabilized by the formation of a cavity in its hydrophobic core. The Pro32Thr allele is thought to cause the observed dominant negative effect because the resulting active enzyme monomer targets both homo- and heterodimers to degradation.
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Affiliation(s)
- Peter D Simone
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Youri I Pavlov
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA; Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, USA; Department of Pathology and Microbiology, University of Nebraska Medical Center, USA; Department of Genetics, St-Petersburg University, St-Petersburg, 199034, Russia
| | - Gloria E O Borgstahl
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA; Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, USA; Department of Pharmaceutical Sciences, University of Nebraska Medical Center, USA.
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26
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Zhao K, Lu ZX, Park JW, Zhou Q, Xing Y. GLiMMPS: robust statistical model for regulatory variation of alternative splicing using RNA-seq data. Genome Biol 2013; 14:R74. [PMID: 23876401 PMCID: PMC4054007 DOI: 10.1186/gb-2013-14-7-r74] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Revised: 06/21/2013] [Accepted: 07/22/2013] [Indexed: 11/10/2022] Open
Abstract
To characterize the genetic variation of alternative splicing, we develop GLiMMPS, a robust statistical method for detecting splicing quantitative trait loci (sQTLs) from RNA-seq data. GLiMMPS takes into account the individual variation in sequencing coverage and the noise prevalent in RNA-seq data. Analyses of simulated and real RNA-seq datasets demonstrate that GLiMMPS outperforms competing statistical models. Quantitative RT-PCR tests of 26 randomly selected GLiMMPS sQTLs yielded a validation rate of 100%. As population-scale RNA-seq studies become increasingly affordable and popular, GLiMMPS provides a useful tool for elucidating the genetic variation of alternative splicing in humans and model organisms.
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Affiliation(s)
- Keyan Zhao
- Department of Microbiology, Immunology, and Molecular Genetics, University of
California, Los Angeles, CHS 33-228, 650 Charles E. Young Drive South, Los
Angeles, CA 90095, USA
- Department of Internal Medicine, University of Iowa, 200 Hawkins Drive, Iowa City,
IA 52242, USA
| | - Zhi-xiang Lu
- Department of Microbiology, Immunology, and Molecular Genetics, University of
California, Los Angeles, CHS 33-228, 650 Charles E. Young Drive South, Los
Angeles, CA 90095, USA
- Department of Internal Medicine, University of Iowa, 200 Hawkins Drive, Iowa City,
IA 52242, USA
| | - Juw Won Park
- Department of Microbiology, Immunology, and Molecular Genetics, University of
California, Los Angeles, CHS 33-228, 650 Charles E. Young Drive South, Los
Angeles, CA 90095, USA
- Department of Internal Medicine, University of Iowa, 200 Hawkins Drive, Iowa City,
IA 52242, USA
| | - Qing Zhou
- Department of Statistics, University of California, Los Angeles, 8125 Math
Sciences Building, Los Angeles, CA 90095, USA
| | - Yi Xing
- Department of Microbiology, Immunology, and Molecular Genetics, University of
California, Los Angeles, CHS 33-228, 650 Charles E. Young Drive South, Los
Angeles, CA 90095, USA
- Department of Internal Medicine, University of Iowa, 200 Hawkins Drive, Iowa City,
IA 52242, USA
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Simone PD, Struble LR, Kellezi A, Brown CA, Grabow CE, Khutsishvili I, Marky LA, Pavlov YI, Borgstahl GE. The human ITPA polymorphic variant P32T is destabilized by the unpacking of the hydrophobic core. J Struct Biol 2013; 182:197-208. [PMID: 23528839 PMCID: PMC4212276 DOI: 10.1016/j.jsb.2013.03.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 03/11/2013] [Accepted: 03/13/2013] [Indexed: 01/24/2023]
Abstract
Inosine triphosphate pyrophosphatase (ITPA), a key enzyme involved in maintaining the purity of cellular nucleoside triphosphate pools, specifically recognizes inosine triphosphate and xanthosine triphosphate (including the deoxyribose forms) and detoxifies them by catalyzing the hydrolysis of a phosphoanhydride bond, releasing pyrophosphate. This prevents their inappropriate use as substrates in enzymatic reactions utilizing (d)ATP or (d)GTP. A human genetic polymorphism leads to the substitution of Thr for Pro32 (P32T) and causes ITPA deficiency in erythrocytes, with heterozygotes having on average 22.5% residual activity, and homozygotes having undetectable activity. This polymorphism has been implicated in modulating patients' response to mercaptopurines and ribavirin. Human fibroblasts containing this variant have elevated genomic instability upon treatment with base analogs. We find that the wild-type and P32T forms are dimeric in solution and in the crystal structure. This abolishes the previous speculation that the P32T change disrupts dimerization as a mechanism of inactivation. The only difference in structure from the wild-type protein is that the area surrounding Thr32 is disrupted. Phe31 is flipped from the hydrophobic core out into the solvent, leaving a hole in the hydrophobic core of the protein which likely accounts for the reduced thermal stability of P32T ITPA and ultimately leads to its susceptibility to degradation in human cells. Circular dichroism and thermal denaturation studies confirm these structural results. We propose that the dimer of P32T variant subunit with wild-type subunit is degraded in cells similarly to the P32T homodimer explaining the level of loss of ITPA activity in heterozygotes.
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Affiliation(s)
- Peter D. Simone
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
| | - Lucas R. Struble
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Admir Kellezi
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
| | - Carrie A. Brown
- Department of Chemistry, Wayne State College, Wayne, NE 68787, USA
| | - Corinn E. Grabow
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
| | - Irine Khutsishvili
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA
| | - Luis A. Marky
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA
| | - Youri I. Pavlov
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Genetics, St-Petersburg University, St-Petersburg 199034, Russia
| | - Gloria E.O. Borgstahl
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA
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Awwad K, Desai A, Smith C, Sommerhalter M. Structural and functional characterization of a noncanonical nucleoside triphosphate pyrophosphatase from Thermotoga maritima. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:184-93. [PMID: 23385455 PMCID: PMC3565439 DOI: 10.1107/s0907444912044630] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Accepted: 10/29/2012] [Indexed: 11/11/2022]
Abstract
The hyperthermophilic bacterium Thermotoga maritima has a noncanonical nucleoside triphosphatase that catalyzes the conversion of inosine triphosphate (ITP), deoxyinosine triphosphate (dITP) and xanthosine triphosphate (XTP) into inosine monophosphate (IMP), deoxyinosine monophosphate (IMP) and xanthosine monophosphate (XMP), respectively. The k(cat)/K(m) values determined at 323 and 353 K fall between 1.31 × 10(4) and 7.80 × 10(4) M(-1) s(-1). ITP and dITP are slightly preferred over XTP. Activity towards canonical nucleoside triphosphates (ATP and GTP) was not detected. The enzyme has an absolute requirement for Mg(2+) as a cofactor and has a preference for alkaline conditions. A protein X-ray structure of the enzyme with bound IMP was obtained at 2.15 Å resolution. The active site houses a well conserved network of residues that are critical for substrate recognition and catalysis. The crystal structure shows a tetramer with two possible dimer interfaces. One of these interfaces strongly resembles the dimer interface that is found in the structures of other noncanonical nucleoside pyrophosphatases from human (human ITPase) and archaea (Mj0226 and PhNTPase).
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Affiliation(s)
- Khaldeyah Awwad
- Chemistry and Biochemistry, California State University East Bay, 25800 Carlos Bee Boulevard, Hayward, CA 94542, USA
| | - Anna Desai
- Chemistry and Biochemistry, California State University East Bay, 25800 Carlos Bee Boulevard, Hayward, CA 94542, USA
| | - Clyde Smith
- Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
| | - Monika Sommerhalter
- Chemistry and Biochemistry, California State University East Bay, 25800 Carlos Bee Boulevard, Hayward, CA 94542, USA
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29
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Waisertreiger ISR, Liston VG, Menezes MR, Kim HM, Lobachev KS, Stepchenkova EI, Tahirov TH, Rogozin IB, Pavlov YI. Modulation of mutagenesis in eukaryotes by DNA replication fork dynamics and quality of nucleotide pools. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2012; 53:699-724. [PMID: 23055184 PMCID: PMC3893020 DOI: 10.1002/em.21735] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Revised: 08/13/2012] [Accepted: 08/15/2012] [Indexed: 06/01/2023]
Abstract
The rate of mutations in eukaryotes depends on a plethora of factors and is not immediately derived from the fidelity of DNA polymerases (Pols). Replication of chromosomes containing the anti-parallel strands of duplex DNA occurs through the copying of leading and lagging strand templates by a trio of Pols α, δ and ϵ, with the assistance of Pol ζ and Y-family Pols at difficult DNA template structures or sites of DNA damage. The parameters of the synthesis at a given location are dictated by the quality and quantity of nucleotides in the pools, replication fork architecture, transcription status, regulation of Pol switches, and structure of chromatin. The result of these transactions is a subject of survey and editing by DNA repair.
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Affiliation(s)
- Irina S.-R. Waisertreiger
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
| | - Victoria G. Liston
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
| | - Miriam R. Menezes
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
| | - Hyun-Min Kim
- School of Biology and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, U.S.A
| | - Kirill S. Lobachev
- School of Biology and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, U.S.A
| | - Elena I. Stepchenkova
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
- Saint Petersburg Branch of Vavilov Institute of General Genetics, Universitetskaya emb. 7/9, St Petersburg, 199034, Russia
- Department of Genetics, Saint Petersburg University, Universitetskaya emb. 7/9, St Petersburg, 199034, Russia
| | - Tahir H. Tahirov
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
| | - Igor B. Rogozin
- National Center for Biotechnology Information NLM, National Institutes of Health, Bethesda, MD 20894, U.S.A
- Institute of Cytology and Genetics, 630090 Novosibirsk, Russia
| | - Youri. I. Pavlov
- Eppley Institute for Research in Cancer and Allied Diseases, ESH 7009, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, U.S.A
- Department of Genetics, Saint Petersburg University, Universitetskaya emb. 7/9, St Petersburg, 199034, Russia
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Schick M, Xie X, Ataka K, Kahnt J, Linne U, Shima S. Biosynthesis of the Iron-Guanylylpyridinol Cofactor of [Fe]-Hydrogenase in Methanogenic Archaea as Elucidated by Stable-Isotope Labeling. J Am Chem Soc 2012; 134:3271-80. [DOI: 10.1021/ja211594m] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Michael Schick
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch Strasse 10, 35043 Marburg, Germany
| | - Xiulan Xie
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein Strasse, 35032 Marburg, Germany
| | - Kenichi Ataka
- Department of Physics, Freie-Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Jörg Kahnt
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch Strasse 10, 35043 Marburg, Germany
| | - Uwe Linne
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein Strasse, 35032 Marburg, Germany
| | - Seigo Shima
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch Strasse 10, 35043 Marburg, Germany
- PRESTO, Japan Science and Technology Agency (JST), Honcho, Kawaguchi, Saitama 332-0012, Japan
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31
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Bakker JA, Lindhout M, Habets DDJ, van den Wijngaard A, Paulussen ADC, Bierau J. The effect of ITPA polymorphisms on the enzyme kinetic properties of human erythrocyte inosine triphosphatase toward its substrates ITP and 6-Thio-ITP. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2011; 30:839-49. [PMID: 22060550 DOI: 10.1080/15257770.2011.606789] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The role of inosine triphosphatase (ITPase) in adverse drug reactions associated with thiopurine therapy is still under heavy debate. Surprisingly, little is known about the way thiopurines are handled by ITPase. We studied the effect of ITPA polymorphisms on the handling of inosine triphosphate (ITP) and thioinosine triphosphate (TITP) to gain more insight into this phenomenon. Human erythrocyte ITPase activity was measured by incubation with ITP using established protocols, and the generated inosine monophosphate (IMP) was measured using ion-pair RP-HPLC. Molecular analysis of the ITPA gene was performed to establish the genotype. Kinetic parameters were established for the two common polymorphisms for both ITP and TITP as substrates using the above mentioned protocol. Both ITP and TITP are substrates for ITPase and their enzyme activities are comparable. Substrate binding is not altered in the different ITPA polymorphisms. It is shown that the velocity of pyrophosphohydrolysis is compromised when the c.94C > A polymorphism is present, both in the heterozygous and in the homozygous state. TITP is handled by ITPase in a similar way as for ITP, which implies that TITP will accumulate in the erythrocytes of patients with an ITPase deficiency, resulting in adverse drug reactions (ADRs) on thiopurine therapy. In carriers of ITPA polymorphisms, the matter is more complex and the development of ADR may depend on additional epigenetic factors rather than on the accumulation of thiopurinenucleotides.
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Affiliation(s)
- Jaap A Bakker
- Laboratory of Biochemical Genetics, Department of Clinical Genetics, Maastricht University Medical Centre, Maastricht, The Netherlands.
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32
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Sakumi K, Abolhassani N, Behmanesh M, Iyama T, Tsuchimoto D, Nakabeppu Y. ITPA protein, an enzyme that eliminates deaminated purine nucleoside triphosphates in cells. Mutat Res 2010; 703:43-50. [PMID: 20601097 DOI: 10.1016/j.mrgentox.2010.06.009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Accepted: 06/13/2010] [Indexed: 12/14/2022]
Abstract
Inosine triphosphate pyrophosphatase (ITPA protein) (EC 3.6.1.19) hydrolyzes deaminated purine nucleoside triphosphates, such as ITP and dITP, to their corresponding purine nucleoside monophosphate and pyrophosphate. In mammals, this enzyme is encoded by the Itpa gene. Using the Itpa gene-disrupted mouse as a model, we have elucidated the biological significance of the ITPA protein and its substrates, ITP and dITP. Itpa(-/-) mice exhibited peri- or post-natal lethality dependent on the genetic background. The heart of the Itpa(-/-) mouse was found to be structurally and functionally abnormal. Significantly higher levels of deoxyinosine and inosine were detected in nuclear DNA and RNA prepared from Itpa(-/-) embryos compared to wild type embryos. In addition, an accumulation of ITP was observed in the erythrocytes of Itpa(-/-) mice. We found that Itpa(-/-) primary mouse embryonic fibroblasts (MEFs), which have no detectable ability to generate IMP from ITP in whole cell extracts, exhibited a prolonged population-doubling time, increased chromosome abnormalities and accumulation of single-strand breaks in their nuclear DNA, in comparison to primary MEFs prepared from wild type embryos. These results revealed that (1) ITP and dITP are spontaneously produced in vivo and (2) accumulation of ITP and dITP is responsible for the harmful effects observed in the Itpa(-/-) mouse. In addition to its effect as the precursor nucleotide for RNA transcription, ITP has the potential to influence the activity of ATP/GTP-binding proteins. The biological significance of ITP and dITP in the nucleotide pool remains to be elucidated.
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Affiliation(s)
- Kunihiko Sakumi
- Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
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Welin M, Nordlund P. Understanding specificity in metabolic pathways--structural biology of human nucleotide metabolism. Biochem Biophys Res Commun 2010; 396:157-63. [PMID: 20494131 DOI: 10.1016/j.bbrc.2010.04.054] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Accepted: 04/08/2010] [Indexed: 10/19/2022]
Abstract
Interactions are the foundation of life at the molecular level. In the plethora of activities in the cell, the evolution of enzyme specificity requires the balancing of appropriate substrate affinity with a negative selection, in order to minimize interactions with other potential substrates in the cell. To understand the structural basis for enzyme specificity, the comparison of structural and biochemical data between enzymes within pathways using similar substrates and effectors is valuable. Nucleotide metabolism is one of the largest metabolic pathways in the human cell and is of outstanding therapeutic importance since it activates and catabolises nucleoside based anti-proliferative drugs and serves as a direct target for anti-proliferative drugs. In recent years the structural coverage of the enzymes involved in human nucleotide metabolism has been dramatically improved and is approaching completion. An important factor has been the contribution from the Structural Genomics Consortium (SGC) at Karolinska Institutet, which recently has solved 33 novel structures of enzymes and enzyme domains in human nucleotide metabolism pathways and homologs thereof. In this review we will discuss some of the principles for substrate specificity of enzymes in human nucleotide metabolism illustrated by a selected set of enzyme families where a detailed understanding of the structural determinants for specificity is now emerging.
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Affiliation(s)
- Martin Welin
- Structural Genomics Consortium, Karolinska Institutet, 17177 Stockholm, Sweden
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Yamamoto K, Okada Y, Nakamura K, Hiromura K, Nojima Y, Nakamura T. Inosine triphosphate pyrophosphatase 94C> A polymorphism: clinical implications for patients with systemic lupus erythematosus treated with azathioprine. Expert Opin Drug Saf 2010; 9:447-57. [DOI: 10.1517/14740330903544474] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Koujirou Yamamoto
- Gunma University Graduate School of Medicine, Department of Clinical Pharmacology, 3-39-22 Showa-machi, Maebashi, Gunma 371-0034, Japan ;
| | - Yuko Okada
- Gunma University Graduate School of Medicine, Department of Clinical Pharmacology, 3-39-22 Showa-machi, Maebashi, Gunma 371-0034, Japan ;
| | - Katsunori Nakamura
- Gunma University Graduate School of Medicine, Department of Clinical Pharmacology, 3-39-22 Showa-machi, Maebashi, Gunma 371-0034, Japan ;
| | - Keiju Hiromura
- Gunma University Graduate School of Medicine, Department of Medicine and Clinical Science, Gunma, Japan
| | - Yoshihisa Nojima
- Gunma University Graduate School of Medicine, Department of Medicine and Clinical Science, Gunma, Japan
| | - Tomonori Nakamura
- Gunma University Graduate School of Medicine, Department of Clinical Pharmacology, 3-39-22 Showa-machi, Maebashi, Gunma 371-0034, Japan ;
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35
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Herting G, Barber K, Zappala MR, Cunningham RP, Burgis NE. Quantitative in vitro and in vivo characterization of the human P32T mutant ITPase. BIOCHIMICA ET BIOPHYSICA ACTA 2010; 1802:269-74. [PMID: 19914375 PMCID: PMC2818573 DOI: 10.1016/j.bbadis.2009.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 10/29/2009] [Accepted: 11/07/2009] [Indexed: 11/29/2022]
Abstract
Human ITPase, encoded by the ITPA gene, and its orthologs (RdgB in Escherichia coli and HAM1 in Saccharomyces cerevisiae) exclude noncanonical nucleoside triphosphates (NTPs) from NTP pools. Deoxyinosine triphosphate (dITP) and 2'-deoxy-N-6-hydroxylaminopurine triphosphate are both hydrolyzed by ITPase to yield the corresponding deoxynucleoside monophosphate and pyrophosphate. In addition, metabolites of thiopurine drugs such as azathioprine have been shown to be substrates for ITPase. The ITPA 94C>A [P32T] variant is one of two polymorphisms associated with decreased ITPase activity. Furthermore, the ITPA 94C>A [P32T] variant is associated with an increased risk of adverse drug reactions for patients treated with azathioprine. The nature of the observed phenotypes for ITPA 94C>A [P32T] variant individuals is currently unclear. Our biochemical assays indicate the P32T ITPase has 55% activity with dITP compared to wild-type ITPase. Complementation experiments at 37 degrees C show that N-6-hydroxylaminopurine sensitivity of E. coli rdgB mutants is reduced with a plasmid bearing the ITPA 94C>A [P32T] gene approximately 50% less than with a plasmid bearing the wild-type ITPA gene. The reduction in sensitivity is less at 42 degrees C. Experiments with synthetic lethal E. coli recA(ts) rdgB mutants show that the ITPA 94C>A [P32T] gene also complements the recA(ts) rdgB growth deficiency at 42 degrees C approximately 40% lower than wild-type ITPA gene. Western blot analysis indicates that the expression level of P32T ITPase is reduced in these cells relative to wild type. Our data support the idea that P32T ITPase is a functional protein, albeit with a reduced rate of noncanonical NTP pyrophosphohydrolase activity and reduced protein stability.
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Affiliation(s)
- Greg Herting
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA 99004
| | - Katie Barber
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA 99004
| | - Maria R. Zappala
- Department of Biological Sciences, The University at Albany, State University of New York, Albany, New York 12222
| | - Richard P. Cunningham
- Department of Biological Sciences, The University at Albany, State University of New York, Albany, New York 12222
| | - Nicholas E. Burgis
- Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA 99004
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Stocco G, Crews KR, Evans WE. Genetic polymorphism of inosine-triphosphate-pyrophosphatase influences mercaptopurine metabolism and toxicity during treatment of acute lymphoblastic leukemia individualized for thiopurine-S-methyl-transferase status. Expert Opin Drug Saf 2010; 9:23-37. [PMID: 20021291 DOI: 10.1517/14740330903426151] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
IMPORTANCE OF THE FIELD Although genetic polymorphisms in the gene encoding human thiopurine methyltransferase (TPMT) are known to have a marked effect on mercaptopurine metabolism and toxicity, there are many patients with wild-type TPMT who develop toxicity. Furthermore, when mercaptopurine dosages are adjusted in patients who are heterozygous at the TPMT locus, there are still some patients who develop toxicity for reasons that are not fully understood. Therefore, we recently studied the effects of a common polymorphism in another gene encoding an enzyme involved in mercaptopurine metabolism (SNP rs1127354 in inosine-triphospate-pyrophosphatase, ITPA), showing that genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of febrile neutropenia following combination chemotherapy of acute lymphoblastic leukemia (ALL) in which mercaptopurine doses are individualized based on TPMT genotype. AREA COVERED IN THIS REVIEW In this review, we summarize the knowledge available about the effect and clinical relevance of TPMT and ITPA on mercaptopurine pharmacogenomics, with a particular focus on the use of this medication in pediatric patients with ALL. WHAT THE READER WILL GAIN Reader will gain insights into: i) the effects of pharmacogenomic traits on mercaptopurine toxicity and efficacy for the treatment of ALL and ii) individualization strategies that can be used to mitigate toxicity without compromising efficacy in pediatric patients with ALL. TAKE HOME MESSAGE Mercaptopurine dose can be adjusted on the basis of TPMT genotype to mitigate toxicity in pediatric patients with ALL. As treatment is individualized in this way for the most relevant genetic determinant of drug response (i.e., for mercaptopurine, TPMT), the importance of other genetic polymorphisms emerges (e.g., ITPA).
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Affiliation(s)
- Gabriele Stocco
- St. Jude Children's Research Hospital, Department of Pharmaceutical Sciences, 262 Danny Thomas Place MS 272, Memphis, TN 38105, USA
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Functional study of the P32T ITPA variant associated with drug sensitivity in humans. J Mol Biol 2009; 392:602-13. [PMID: 19631656 DOI: 10.1016/j.jmb.2009.07.051] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2009] [Revised: 07/15/2009] [Accepted: 07/16/2009] [Indexed: 12/12/2022]
Abstract
Sanitization of the cellular nucleotide pools from mutagenic base analogues is necessary for the accuracy of transcription and replication of genetic material and plays a substantial role in cancer prevention. The undesirable mutagenic, recombinogenic, and toxic incorporation of purine base analogues [i.e., ITP, dITP, XTP, dXTP, or 6-hydroxylaminopurine (HAP) deoxynucleoside triphosphate] into nucleic acids is prevented by inosine triphosphate pyrophosphatase (ITPA). The ITPA gene is a highly conserved, moderately expressed gene. Defects in ITPA orthologs in model organisms cause severe sensitivity to HAP and chromosome fragmentation. A human polymorphic allele, 94C-->A, encodes for the enzyme with a P32T amino acid change and leads to accumulation of non-hydrolyzed ITP. ITPase activity is not detected in erythrocytes of these patients. The P32T polymorphism has also been associated with adverse sensitivity to purine base analogue drugs. We have found that the ITPA-P32T mutant is a dimer in solution, as is wild-type ITPA, and has normal ITPA activity in vitro, but the melting point of ITPA-P32T is 5 degrees C lower than that of wild-type. ITPA-P32T is also fully functional in vivo in model organisms as determined by a HAP mutagenesis assay and its complementation of a bacterial ITPA defect. The amount of ITPA protein detected by Western blot is severely diminished in a human fibroblast cell line with the 94C-->A change. We propose that the P32T mutation exerts its effect in certain human tissues by cumulative effects of destabilization of transcripts, protein stability, and availability.
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Stocco G, Cheok MH, Crews KR, Dervieux T, French D, Pei D, Yang W, Cheng C, Pui CH, Relling MV, Evans WE. Genetic polymorphism of inosine triphosphate pyrophosphatase is a determinant of mercaptopurine metabolism and toxicity during treatment for acute lymphoblastic leukemia. Clin Pharmacol Ther 2008; 85:164-72. [PMID: 18685564 DOI: 10.1038/clpt.2008.154] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The influence of genetic polymorphism in inosine triphosphate pyrophosphatase (ITPA) on thiopurine-induced adverse events has not been investigated in the context of combination chemotherapy for acute lymphoblastic leukemia (ALL). This study investigated the effects of a common ITPA variant allele (rs41320251) on mercaptopurine metabolism and toxicity during treatment of children with ALL. Significantly higher concentrations of methyl mercaptopurine nucleotides were found in patients with the nonfunctional ITPA allele. Moreover, there was a significantly higher probability of severe febrile neutropenia in patients with a variant ITPA allele among patients whose dose of mercaptopurine had been adjusted for TPMT genotype. In a cohort of patients whose mercaptopurine dose was not adjusted for TPMT phenotype, the TPMT genotype had a greater effect than the ITPA genotype. In conclusion, genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of severe febrile neutropenia, after combination chemotherapy for ALL in which mercaptopurine doses are individualized on the basis of TPMT genotype.
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Affiliation(s)
- G Stocco
- Department of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, Tennessee, USA
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Structural genomics and drug discovery: all in the family. Curr Opin Chem Biol 2008; 12:32-9. [PMID: 18282486 DOI: 10.1016/j.cbpa.2008.01.045] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 01/23/2008] [Accepted: 01/28/2008] [Indexed: 11/22/2022]
Abstract
Structural genomics is starting to have an impact on the early stages of drug discovery and target validation through the contribution of new structures of known and potential drug targets, their complexes with ligands and protocols and reagents for additional structural work within a drug discovery program. Recent progress includes structures of targets from bacterial, viral and protozoan human pathogens, and human targets from known or potential druggable protein families such as, kinases, phosphatases, dehydrogenases/oxidoreductases, sulfo-, acetyl- and methyl-transferases, and a number of other key metabolic enzymes. Importantly, many of these structures contained ligands in the active sites, including for example, the first structures of target-bound therapeutics. Structural genomics of protein families combined with ligand discovery holds particular promise for advancing early stage discovery programs.
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Lokanath NK, Pampa KJ, Takio K, Kunishima N. Structures of dimeric nonstandard nucleotide triphosphate pyrophosphatase from Pyrococcus horikoshii OT3: functional significance of interprotomer conformational changes. J Mol Biol 2008; 375:1013-25. [PMID: 18062990 DOI: 10.1016/j.jmb.2007.11.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2007] [Revised: 10/30/2007] [Accepted: 11/06/2007] [Indexed: 10/22/2022]
Abstract
Nonstandard nucleotide triphosphate pyrophosphatase (NTPase) can efficiently hydrolyze nonstandard purine nucleotides in the presence of divalent cations. The crystal structures of the NTPase from Pyrococcus horikoshii OT3 (PhNTPase) have been determined in two unliganded forms and in three liganded forms with inosine 5'-monophosphate (IMP), ITP and Mn(2+), which visualize the recognition of these ligands unambiguously. The overall structure of PhNTPase is similar to that of previously reported crystal structures of the NTPase from Methanococcus jannaschii and the human ITPase. They share a similar protomer folding with two domains and a similar homodimeric quaternary structure. The dimeric interface of NTPase is well conserved, and the dimeric state might be important to constitute the active site of this enzyme. A conformational analysis of the five snapshots of PhNTPase structures using the multiple superposition method reveals that IMP, ITP and Mn(2+) bind to the active site without inducing large local conformational changes, indicating that a combination of interdomain and interprotomer rigid-body shifts mainly describes the conformational change of PhNTPase. The interdomain and interprotomer conformations of the ITP liganded form are essentially the same as those observed in the unliganded form 1, indicating that ITP binding to PhNTPase in solution may follow the selection mode in which ITP binds to the subunit that happens to be in the conformation observed in the unliganded form 1. In contrast to the human ITPase inducing a large domain closure upon ITP binding, the interdomain active site cleft is generally closed in PhNTPase and only the IMP binding form shows a remarkable domain opening by 14 degrees only in the B subunit. The interprotomer rigid-body rotation of PhNTPase has a tendency to keep the dimeric 2-fold symmetry, which is also true in human ITPase, thereby suggesting its relevance to the positive cooperativity of the dimeric NTPases. The exception of this rule is observed in the IMP liganded form in which the dimeric 2-fold symmetry is broken by a 3 degrees interprotomer rotation in an unusual direction. A combination of the exceptional interdomain and interprotomer relocations is most likely the reason for the observed asymmetric IMP binding that might be necessary for PhNTPase to release the reaction product IMP.
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MESH Headings
- Amino Acid Sequence
- Base Sequence
- Binding Sites
- Cations, Divalent/metabolism
- Conserved Sequence
- Crystallography, X-Ray
- Dimerization
- Escherichia coli/genetics
- Hydrogen Bonding
- Hydrolysis
- Inosine Monophosphate/metabolism
- Ligands
- Light
- Manganese/metabolism
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Plasmids
- Protein Binding
- Protein Conformation
- Protein Folding
- Protein Structure, Quaternary
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Pyrococcus horikoshii/chemistry
- Pyrococcus horikoshii/enzymology
- Pyrophosphatases/chemistry
- Pyrophosphatases/genetics
- Pyrophosphatases/metabolism
- Recombinant Proteins/chemistry
- Recombinant Proteins/metabolism
- Rotation
- Scattering, Radiation
- Sequence Homology, Amino Acid
- Synchrotrons
- Transformation, Bacterial
- Water/chemistry
- X-Ray Diffraction
- Inosine Triphosphatase
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Affiliation(s)
- Neratur K Lokanath
- Advanced Protein Crystallography Research Group, RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
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Savchenko A, Proudfoot M, Skarina T, Singer A, Litvinova O, Sanishvili R, Brown G, Chirgadze N, Yakunin AF. Molecular basis of the antimutagenic activity of the house-cleaning inosine triphosphate pyrophosphatase RdgB from Escherichia coli. J Mol Biol 2007; 374:1091-103. [PMID: 17976651 DOI: 10.1016/j.jmb.2007.10.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 10/03/2007] [Accepted: 10/04/2007] [Indexed: 11/17/2022]
Abstract
Inosine triphosphate pyrophosphatases, which are ubiquitous house-cleaning enzymes, hydrolyze noncanonical nucleoside triphosphates (inosine triphosphate (ITP) and xanthosine triphosphate (XTP)) and prevent the incorporation of hypoxanthine or xanthine into nascent DNA or RNA. Here we present the 1.5-A-resolution crystal structure of the inosine triphosphate pyrophosphatase RdgB from Escherichia coli in a free state and in complex with a substrate (ITP+Ca(2+)) or a product (inosine monophosphate (IMP)). ITP binding to RdgB induced a large displacement of the alpha1 helix, closing the enzyme active site. This positions the conserved Lys13 close to the bridging oxygen between the alpha- and beta-phosphates of the substrate, weakening the P(alpha)-O bond. On the other side of the substrate, the conserved Asp69 is proposed to act as a base coordinating the catalytic water molecule. Our data provide insight into the molecular mechanisms of the substrate selectivity and catalysis of RdgB and other ITPases.
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Affiliation(s)
- Alexei Savchenko
- Banting and Best Department of Medical Research and Ontario Center for Structural Proteomics, University of Toronto, 112 College Street, Toronto, Ontario, Canada M5G 1L6
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Takayama S, Fujii M, Kurosawa A, Adachi N, Ayusawa D. Overexpression of HAM1 gene detoxifies 5-bromodeoxyuridine in the yeast Saccharomyces cerevisiae. Curr Genet 2007; 52:203-11. [PMID: 17899088 DOI: 10.1007/s00294-007-0152-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2007] [Revised: 08/23/2007] [Accepted: 08/28/2007] [Indexed: 11/28/2022]
Abstract
5-Bromodeoxyuridine (BrdU) is known to modulate expression of particular genes, and eventually arrest cell division in mammalian and yeast cells. To study a molecular basis for these phenomena, we adopted a genetic approach with a yeast cell system. We screened multicopy suppressor genes that confer resistance to BrdU with a thymidine-auxotrophic strain of the yeast Saccharomyces cerevisiae. One of such genes was found to encode Ham1 protein, which was originally identified as a possible triphosphatase for N-6-hydroxylaminopurine triphosphate. Consistent with this, overexpression of the HAM1 gene reversed growth arrest caused by BrdU, and blocked incorporation of BrdU into genomic DNA. On the contrary, disruption of the gene sensitized cells to BrdU. A crude extract from Ham1-overproducing cells showed a high activity to hydrolyze BrdUTP to BrdUMP and pyrophosphate in addition to abnormal purine nucleotides. Purified recombinant Ham1 protein showed the same activity. These results demonstrate that Ham1 protein detoxifies abnormal pyrimidine as well as purine nucleotides.
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Affiliation(s)
- Shinichi Takayama
- Kihara Institute for Biological Research and Graduate School of Integrated Science, Yokohama City University, Maioka-cho 641-12, Yokohama 244-0813, Japan
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Abstract
Inosine triphosphatase (ITPase) is the enzyme that catalyzes the conversion of inosine triphosphate (ITP) and deoxy-inosine triphosphate (dITP) to inosine monophosphate and deoxy-inosine monophosphate, respectively, thereby maintaining low intracellular concentrations of ITP and dITP. Individuals deficient in ITPase activity were first recognized over 30 years ago. For decades, no clinical significance could be attributed to this inborn error of metabolism whatsoever. In recent years, evidence has started to accumulate that polymorphisms in the gene encoding ITPase are associated with potentially severe adverse drug reactions towards the thiopurine drugs azathioprine and 6-mercaptopurine. The pharmacogenetic significance is presently being debated in the literature. However, the present state of knowledge is still insufficient to definitively determine the pharmacogenetic significance of ITPase. This article aims to review the current knowledge on the role of ITPase in thiopurine metabolism.
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Affiliation(s)
- Jörgen Bierau
- Maastricht University Hospital, Laboratory of Biochemical Genetics, Department of Clinical Genetics, PO Box 6202 AZ Maastricht, The Netherlands.
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