Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have cloned and expressed the full-length gene encoding the hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRTase) from the anaerobic protozoan parasite Tritrichomonas foetus. This enzyme is essential in nucleic acid metabolism of T. foetus because the parasite is unable to synthesize purine nucleotides de novo and relies on the HGXPRTase activities for its purine requirements. Initially, a cDNA clone encoding part of the HGXPRTase was isolated by complementation of an Escherichia coli mutant, SO609, with a cDNA library of T. foetus. Northern blot analysis identified a single mRNA band of approximately 700-800 bases. The full-length genomic clone was then isolated and identified to have an open reading frame of 549 bp encoding an 183-amino acid sequence with an estimated size of 21.1 kDa. The sequence is only 27.3% identical to that of the human HGPRTase. The T. foetus HGXPRTase gene was subsequently cloned into the pBAce vector for expression in E. coli. This construct yields completely soluble and enzymatically active recombinant T. foetus HGXPRTase, which constitutes approximately 20% of the total cellular protein of the transformed E. coli. It has the same molecular weight as the authentic native enzyme, and the N-terminal amino acid sequence of the recombinant enzyme is identical to that predicted from the open reading frame. The high expression of this apparently native T. foetus HGXPRTase will provide large quantities of purified protein, necessary for detailed kinetic and structural analysis of this enzyme for its potential value as a target for antitrichomonial chemotherapy. To our knowledge, this is also the first time a gene from T. foetus was cloned and expressed.
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PMID:Isolation, sequencing and expression of the gene encoding hypoxanthine-guanine-xanthine phosphoribosyltransferase of Tritrichomonas foetus. 800 20

Xanthine phosphoribosyltransferase (XPRT) from Leishmania donovani is a unique enzyme that lacks a mammalian counterpart and is, therefore, a potential target for antiparasitic therapy. To investigate the enzyme at the molecular and biochemical level, a cDNA encoding the L. donovani XPRT was isolated by functional complementation of a purine auxotroph of Escherichia coli that also harbors deficiencies in the prokaryotic phosphoribosyltransferase (PRT) activities. The cDNA was then used to isolate the XPRT genomic clone. XPRT encodes a 241-amino acid protein exhibiting approximately 33% amino acid identity with the L. donovani hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and significant homology with other HGPRT family members. Southern blot analysis revealed that XPRT was a single copy gene that co-localized with HGPRT within a 4.3-kilobase pair (kb) EcoRI fragment, implying that the two genes arose as a result of an ancestral duplication event. Sequencing of this EcoRI fragment confirmed that HGPRT and XPRT were organized in a head-to-tail arrangement separated by an approximately 2.2-kb intergenic region. Both the 3.2-kb XPRT mRNA and XPRT enzyme were significantly up-regulated in Deltahgprt and Deltahgprt/Deltaaprt L. donovani mutants. Genetic obliteration of the XPRT locus by targeted gene replacement indicated that XPRT was not an essential gene under most conditions and that the Deltaxprt null strain was competent of salvaging all purines except xanthine. XPRT was overexpressed in E. coli and the recombinant protein purified to homogeneity. Kinetic analysis revealed that the XPRT preferentially phosphoribosylated xanthine but could also recognize hypoxanthine and guanine. K(m) values of 7.1, 448.0, and >100 microM and k(cat) values of 3.5, 2.6, and approximately 0.003 s(-1) were calculated for xanthine, hypoxanthine, and guanine, respectively. The XPRT gene and XPRT protein provide the requisite molecular and biochemical reagents for subsequent studies to validate XPRT as a potential therapeutic target.
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PMID:Xanthine phosphoribosyltransferase from Leishmania donovani. Molecular cloning, biochemical characterization, and genetic analysis. 1056 19