2i5d
Crystal Structure of Human Inosine Triphosphate Pyrophosphatase
Structural highlights
DiseaseITPA_HUMAN Defects in ITPA are the cause of inosine triphosphate pyrophosphohydrolase deficiency (ITPAD) [MIM:613850. It is a common inherited trait characterized by the abnormal accumulation of inosine triphosphate (ITP) in erythrocytes and also leukocytes and fibroblasts. The pathological consequences of ITPA deficiency, if any, are unknown. However, it might have pharmacogenomic implications and be related to increased drug toxicity of purine analog drugs. Note=Three different human populations have been reported with respect to their ITPase activity: high, mean (25% of high) and low activity. The variant Thr-32 is associated with complete loss of enzyme activity, may be by altering the local secondary structure of the protein. Heterozygotes for this polymorphism have 22.5% of the control activity: this is consistent with a dimeric structure of the enzyme.[:][1] [2] FunctionITPA_HUMAN Pyrophosphatase that hydrolyzes the non-canonical purine nucleotides inosine triphosphate (ITP), deoxyinosine triphosphate (dITP) as well as 2'-deoxy-N-6-hydroxylaminopurine triposphate (dHAPTP) and xanthosine 5'-triphosphate (XTP) to their respective monophosphate derivatives. The enzyme does not distinguish between the deoxy- and ribose forms. Probably excludes non-canonical purines from RNA and DNA precursor pools, thus preventing their incorporation into RNA and DNA and avoiding chromosomal lesions.[3] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe structure of human inosine triphosphate pyrophosphohydrolase (ITPA) has been determined using diffraction data to 1.6 A resolution. ITPA contributes to the accurate replication of DNA by cleansing cellular dNTP pools of mutagenic nucleotide purine analogs such as dITP or dXTP. A similar high-resolution unpublished structure has been deposited in the Protein Data Bank from a monoclinic and pseudo-merohedrally twinned crystal. Here, cocrystallization of ITPA with a molar ratio of XTP appears to have improved the crystals by eliminating twinning and resulted in an orthorhombic space group. However, there was no evidence for bound XTP in the structure. Comparison with substrate-bound NTPase from a thermophilic organism predicts the movement of residues within helix alpha1, the loop before alpha6 and helix alpha7 to cap off the active site when substrate is bound. Structure of the orthorhombic form of human inosine triphosphate pyrophosphatase.,Porta J, Kolar C, Kozmin SG, Pavlov YI, Borgstahl GE Acta Crystallogr Sect F Struct Biol Cryst Commun. 2006 Nov 1;62(Pt, 11):1076-81. Epub 2006 Oct 25. PMID:17077483[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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