1
|
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.
Collapse
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
| |
Collapse
|
2
|
Schroader JH, Handley MT, Reddy K. Inosine triphosphate pyrophosphatase: A guardian of the cellular nucleotide pool and potential mediator of RNA function. WILEY INTERDISCIPLINARY REVIEWS. RNA 2023; 14:e1790. [PMID: 37092460 DOI: 10.1002/wrna.1790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 02/10/2023] [Accepted: 03/20/2023] [Indexed: 04/25/2023]
Abstract
Inosine triphosphate pyrophosphatase (ITPase), encoded by the ITPA gene in humans, is an important enzyme that preserves the integrity of cellular nucleotide pools by hydrolyzing the noncanonical purine nucleotides (deoxy)inosine and (deoxy)xanthosine triphosphate into monophosphates and pyrophosphate. Variants in the ITPA gene can cause partial or complete ITPase deficiency. Partial ITPase deficiency is benign but clinically relevant as it is linked to altered drug responses. Complete ITPase deficiency causes a severe multisystem disorder characterized by seizures and encephalopathy that is frequently associated with fatal infantile dilated cardiomyopathy. In the absence of ITPase activity, its substrate noncanonical nucleotides have the potential to accumulate and become aberrantly incorporated into DNA and RNA. Hence, the pathophysiology of ITPase deficiency could arise from metabolic imbalance, altered DNA or RNA regulation, or from a combination of these factors. Here, we review the known functions of ITPase and highlight recent work aimed at determining the molecular basis for ITPA-associated pathogenesis which provides evidence for RNA dysfunction. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.
Collapse
Affiliation(s)
- Jacob H Schroader
- The RNA Institute, University at Albany, State University of New York, Albany, New York, USA
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
| | - Mark T Handley
- Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Kaalak Reddy
- The RNA Institute, University at Albany, State University of New York, Albany, New York, USA
- Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
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.
Collapse
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
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
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.
Collapse
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
| |
Collapse
|
7
|
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.
Collapse
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
| |
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
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.
Collapse
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
| |
Collapse
|
10
|
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.
Collapse
Affiliation(s)
- Nicholas E Burgis
- Department of Chemistry and Biochemistry, Eastern Washington University, 226 Science Building, Cheney, WA, 99004, USA.
| |
Collapse
|
11
|
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.
Collapse
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
| |
Collapse
|
12
|
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.
Collapse
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
| | | | | |
Collapse
|