Publications

• Uridine-ribohydrolase is a key regulator in the uridine degradation pathway of Arabidopsis.

  Jung B., Florchinger M., Kunz H.H., Traub M., Wartenberg R., Jeblick W., Neuhaus H.E., Mohlmann T.

  Nucleoside degradation and salvage are important metabolic pathways but hardly understood in plants. Recent work on human pathogenic protozoans like Leishmania and Trypanosoma substantiates an essential function of nucleosidase activity. Plant nucleosidases are related to those from protozoans and ... >> More

  Nucleoside degradation and salvage are important metabolic pathways but hardly understood in plants. Recent work on human pathogenic protozoans like Leishmania and Trypanosoma substantiates an essential function of nucleosidase activity. Plant nucleosidases are related to those from protozoans and connect the pathways of nucleoside degradation and salvage. Here, we describe the cloning of such an enzyme from Arabidopsis thaliana, Uridine-Ribohydrolase 1 (URH1) and the characterization by complementation of a yeast mutant. Furthermore, URH1 was synthesized as a recombinant protein in Escherichia coli. The pure recombinant protein exhibited highest hydrolase activity for uridine, followed by inosine and adenosine, the corresponding K(m) values were 0.8, 1.4, and 0.7 mM, respectively. In addition, URH1 was able to cleave the cytokinin derivative isopentenyladenine-riboside. Promoter beta-glucuronidase fusion studies revealed that URH1 is mainly transcribed in the vascular cells of roots and in root tips, guard cells, and pollen. Mutants expressing the Arabidopsis enzyme or the homolog from rice (Oryza sativa) exhibit resistance toward toxic fluorouridine, fluorouracil, and fluoroorotic acid, providing clear evidence for a pivotal function of URH1 as regulative in pyrimidine degradation. Moreover, mutants with increased and decreased nucleosidase activity are delayed in germination, indicating that this enzyme activity must be well balanced in the early phase of plant development. << Less

  Plant Cell 21:876-891(2009) [PubMed] [EuropePMC]

• The URH1 uridine ribohydrolase of Saccharomyces cerevisiae.

  Kurtz J.-E., Exinger F., Erbs P., Jund R.

  In the yeast Saccharomyces cerevisiae, uridine ribohydrolase activity is important for recycling, via the salvage pathway, pyrimidine deoxy- and ribonucleosides into uracil required for the growth of strains lacking the de novo pyrimidine synthesis pathway. We have shown that not only uridine and ... >> More

  In the yeast Saccharomyces cerevisiae, uridine ribohydrolase activity is important for recycling, via the salvage pathway, pyrimidine deoxy- and ribonucleosides into uracil required for the growth of strains lacking the de novo pyrimidine synthesis pathway. We have shown that not only uridine and cytidine, but also 5-fluorouridine, 5-fluorocytidine and deoxycytidine are substrates for this enzyme. We identified, cloned and characterized the corresponding URH1 gene and its physiological function was determined by the measurement of metabolic fluxes in several mutants impaired in the pyrimidine salvage pathway. Sequence comparison revealed strong homology between Urh1p and the inosine/uridine-preferring nucleosidase and inosine/adenosine/guanosine nucleoside hydrolase proteins from the parasitic organisms Crithidia fasciculata and Trypanosoma brucei brucei. Moreover, the Asp and His residues in the putative active site were conserved. Site-directed mutagenesis demonstrated that the conserved His residue is involved in catalysis. These results allow us to speculate that the structure and catalytic mechanism of Urh1p are similar to the inosine/uridine nucleoside hydrolase from C. fasciculata. << Less

  Curr. Genet. 41:132-141(2002) [PubMed] [EuropePMC]

• Crystal structure to 1.7 A of the Escherichia coli pyrimidine nucleoside hydrolase YeiK, a novel candidate for cancer gene therapy.

  Giabbai B., Degano M.

  Enzymes with nucleoside hydrolase (NH) activity are crucial for salvaging nucleic acid components in purine auxotrophic protozoan parasites, but are also present in prokaryotes and higher eukaryotes. Here we analyze the distribution of genes encoding for putative NH proteins and characterize the y ... >> More

  Enzymes with nucleoside hydrolase (NH) activity are crucial for salvaging nucleic acid components in purine auxotrophic protozoan parasites, but are also present in prokaryotes and higher eukaryotes. Here we analyze the distribution of genes encoding for putative NH proteins and characterize the yeiK gene product from Escherichia coli as a pyrimidine-specific NH. The crystal structure of YeiK to 1.7 A defines the structural basis for its substrate specificity and identifies residues involved in the catalytic mechanism that differ from both nonspecific and purine-specific NHs. Large differences in the tetrameric quaternary structure compared to nonspecific protozoan NHs are brought forth by minor differences in the interacting surfaces. The first structural and functional characterization of a nonparasitic, pyrimidine nucleoside-specific NH suggests a possible role for these enzymes in the metabolism of tRNA nucleosides. The high catalytic efficiency of YeiK toward 5-fluorouridine could be exploited for suicide gene therapy in cancer treatment. << Less

  Structure 12:739-749(2004) [PubMed] [EuropePMC]

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