Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.2.7 (adenine phosphoribosyltransferase)
 692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRTase) from Tritrichomonas foetus has been proven to be a target for potential anti-tritrichomonial chemotherapy. Using a structure-based approach, the base-binding region of the active site of this enzyme, which confers unique purine base specificity, was characterized using site-directed mutagenesis. Determining the roles of different active-site residues in purine specificity would form the basis for designing specific inhibitors toward the parasitic enzyme. A D163N mutant converts the HGXPRTase into a HGPRTase, which no longer recognizes xanthine as a substrate, whereas specificities toward guanine and hypoxanthine are unaffected. Apparently, the side-chain carboxyl of Asp163 forms a hydrogen bond through a water molecule with the C2-carbonyl of xanthine, which constitutes the critical force enabling the enzyme to recognize xanthine as a substrate. Mutations of Arg155, which orients and stacks the neighboring Tyr156 onto the bound purine base by forming a salt bridge between itself and Glu11, result in drastic increases in the Kms for GMP and XMP (but not IMP). This change leads to increased kcats for the forward reactions with guanine and xanthine as substrates without affecting the conversion of hypoxanthine to IMP. Thus, the apparent dislocation of Tyr156, resulted from mutations of Arg155, bring little effect on the hydrophobic interactions between Tyr156 and the purine ring. But the forces involved in recognizing the exocyclic C2-substituents of the purine ring, which involve the Tyr156 hydroxyl, Ile157 backbone carbonyl, and Asp163 side-chain carboxyl, may be weakened by the shifted conformation of the peptide backbone resulted from loss of the Glu11-Arg155 salt bridge. The conserved Lys134 was proven to be the primary determinant in conferring the specificity of the enzyme toward 6-oxopurines. By substituting the lysine residue for a serine, which can potentially hydrogen bond to either an amino or an oxo-group, we have successfully augmented the purine specificity of the enzyme. The K134S mutant recognizes adenine in addition to hypoxanthine, guanine, and xanthine as its substrates. Adenine and hypoxanthine are equivalent substrates for the mutant enzyme with similar Kms of 34.6 and 38.0 microM, respectively. The catalysis of an adenine phosphoribosyltransferase reaction by this mutant enzyme was further demonstrated by the competitive inhibition of AMP with an estimated Kis of 25.4 microM against alpha-D-5-phosphoribosyl-pyrophosphate (PRPP) in converting hypoxanthine to IMP. We have thus succeeded in using site-directed mutagenesis to convert T. foetusHGXPRTase into either a HGPRTase or a genuine AHGXPRTase.
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PMID:Altering the purine specificity of hypoxanthine-guanine-xanthine phosphoribosyltransferase from Tritrichomonas foetus by structure-based point mutations in the enzyme protein. 984 28

Carbon nanotubes (CNTs) have shown promise as an important new class of multifunctional building blocks and innovative tools in a large variety of applications, ranging from nanocomposite materials through nanoelectronics to biomedical devices. Because of their unusual one-dimensional hollow nanostructure and unique physicochemical properties, CNTs are particularly useful as novel drug delivery tools and imaging agents. However, such biomedical applications will not be realized if there is no proper assessment of the potential hazards of CNTs to humans and other biological systems. Although a few reports on the cytotoxicity of CNTs have been published, very little is known about the toxicity at the molecular level, or genotoxicity, of CNTs in mammalian cells. We have for the first time assessed the DNA damage response to multiwalled carbon nanotubes (MWNTs) in mouse embryonic stem (ES) cells. We found that MWNTs can accumulate and induce apoptosis in mouse ES cells and activate the tumor suppressor protein p53 within 2 h of exposure. Furthermore, we also observed increased expression of two isoforms of base excision repair protein 8-oxoguanine-DNA glycosylase 1 (OGG1), double strand break repair protein Rad 51, phosphorylation of H2AX histone at serine 139, and SUMO modification of XRCC4 following the treatment with MWNTs. A mutagenesis study using an endogenous molecular marker, adenine phosphoribosyltransferase (Aprt), showed that MWNTs increased the mutation frequency by 2-fold compared with the spontaneous mutation frequency in mouse ES cells. These results suggest that careful scrutiny of the genotoxicity of nanomaterials is needed even for those materials, like multiwalled carbon nanotubes, that have been previously demonstrated to have limited or no toxicity at the cellular level.
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PMID:DNA damage induced by multiwalled carbon nanotubes in mouse embryonic stem cells. 1804 46

We present the first proteomic analysis on the cellular responses to avian influenza virus (H9N2) infection in a human cell line in different time courses in order to search for target proteins for viral pathogenesis/adaptation studies. By using 2-DE coupled with MALDI-TOF MS and nano-ESI-MS/MS, we identified a set of differentially expressed cellular proteins, including cytoplasmic actin, cytokeratin, prohibitin, enoyl-CoA hydratase, peptide-prolyl cis-trans isomerase A (PPIase A), chloride intracellular channel protein 1, pyruvate dehydrogenase E1 component subunit beta, adenine phosphoribosyltransferase, guanine nucleotide-binding protein subunit beta, nucleoside diphosphate kinase A, elongation factor 1-beta and splicing factor, arginine/serine rich 1. The most significant changes in different time courses were found in cytoplasmic actin and cytokeratin, both of which constituted the major components of cytoskeleton network in the cells. The obtained data suggested a possible role of the cytoskeleton during avian influenza virus infection of mammalian cells, which might help for better understanding of the dynamics of avian influenza virus and host interaction in mammalian cell setting.
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PMID:Proteomics analysis of differential expression of cellular proteins in response to avian H9N2 virus infection in human cells. 1839 75

A metabolomic analysis of plasma amino acids and acylcarnitines was applied to four disorders of nucleotide metabolism. Multivariate analysis gave score plots that show segregation of hypoxanthine phosphoribosyltransferase and adenine phosphoribosyltransferase deficient plasma from controls with equivocal results for adenosine deaminase and dihydropyrimidine dehydrogenase deficiencies. Loadings plots revealed the principal metabolites responsible for the discrimination between these classes. There were increases for HPRT in C4-, C6-, and C3-DC (malonyl)-carnitines, and decreased serine. For APRT there were increases in C4- to C10- and C3-DC to C6-DC-carnitines, urea, 1-methylhistidine, 3-methylhistidine, and decreased tryptophan. For ADA deficiency there were increases in C4- and C6-carnitines, taurine, and isoleucine.
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PMID:Application of metabolomic principles to disorders of nucleotide metabolism reveals new metabolic perturbations. 1860 May 20