title: Characterization of pyrimidine nucleoside phosphorylase of Mycoplasma hyorhinis: implications for the clinical efficacy of nucleoside analogues.
abstract: In the present paper we demonstrate that the cytostatic and antiviral activity of pyrimidine nucleoside analogues is markedly decreased by a Mycoplasma hyorhinis infection and show that the phosphorolytic activity of the mycoplasmas is responsible for this. Since mycoplasmas are (i) an important cause of secondary infections in immunocompromised (e.g. HIV infected) patients and (ii) known to preferentially colonize tumour tissue in cancer patients, catabolic mycoplasma enzymes may compromise efficient chemotherapy of virus infections and cancer. In the genome of M. hyorhinis, a TP (thymidine phosphorylase) gene has been annotated. This gene was cloned, expressed in Escherichia coli and kinetically characterized. Whereas the mycoplasma TP efficiently catalyses the phosphorolysis of thymidine (Km=473 μM) and deoxyuridine (Km=578 μM), it prefers uridine (Km=92 μM) as a substrate. Our kinetic data and sequence analysis revealed that the annotated M. hyorhinis TP belongs to the NP (nucleoside phosphorylase)-II class PyNPs (pyrimidine NPs), and is distinct from the NP-II class TP and NP-I class UPs (uridine phosphorylases). M. hyorhinis PyNP also markedly differs from TP and UP in its substrate specificity towards therapeutic nucleoside analogues and susceptibility to clinically relevant drugs. Several kinetic properties of mycoplasma PyNP were explained by in silico analyses.
authors.affiliation: Rega Institute for Medical Research, KU Leuven, Minderbroedersstraat 10, blok x - bus 1030, B-3000 Leuven, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Vande Voorde
authors.forename: Federico
authors.initials: F
authors.lastname: Gago
authors.forename: Kristof
authors.initials: K
authors.lastname: Vrancken
authors.forename: Sandra
authors.initials: S
authors.lastname: Liekens
authors.forename: Jan
authors.initials: J
authors.lastname: Balzarini
mesh_terms: D000595:Amino Acid Sequence; D000998:Antiviral Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000821:virology*; D001973:Bromodeoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology; D019295:Computational Biology; D005260:Female; D006801:Humans; D007065:Idoxuridine / Q000494:pharmacology; D007700:Kinetics; D008969:Molecular Sequence Data; D009175:Mycoplasma Infections; D045790:Mycoplasma hyorhinis / Q000201:enzymology*; D011487:Protein Conformation; D011741:Pyrimidine Nucleosides / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013939:Thymidine Phosphorylase / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014543:Uridine Phosphorylase / Q000378:metabolism*; D014780:Viruses / Q000187:drug effects
chemical_list: D000998:Antiviral Agents; D011741:Pyrimidine Nucleosides; C020235:brivudine; D014543:Uridine Phosphorylase; D013939:Thymidine Phosphorylase; D001973:Bromodeoxyuridine; D007065:Idoxuridine