deoxyguanosine-triphosphate and 8-hydroxyguanine

The formation of binary Ni(II) complexes with 2'-deoxyguanosine 5'-triphosphate (dGTP, L) as well as ternary complexes thereof with L-histidine (His, A) was studied with the use of potentiometry and electronic absorption spectroscopy. In the binary and ternary systems, the complexes with stoichiometries NiH2L-, NiHL2-, NiL3- and NiH2LA2-, NiHLA3-, NiLA4- respectively, were detected. The ternary complexes are very stable at pH 7.4 and thus may constitute biologically relevant Ni(II) carriers in the cell. In the presence of hydrogen peroxide, the binary and ternary systems both generate hydroxyl radical-like species and undergo dGTP degradation with the formation of the 8-oxo-dGTP intermediate. The latter, along with dGTP complexation and degradation, may lead to mutagenesis and carcinogenesis due to base-mispairing properties of 8-oxoguanine and the disturbance in the physiological balance among the four canonical triphosphodeoxynucleotide substrates for DNA synthesis.

Topics: Base Pairing; Carcinogens; Cations, Divalent; Chromatography, High Pressure Liquid; Deoxyguanine Nucleotides; DNA; Drug Stability; Guanine; Histidine; Hydrogen-Ion Concentration; Molecular Structure; Mutagenesis; Nickel; Nucleotides; Oxidation-Reduction; Potentiometry; Spectrophotometry; Time Factors

8-OxoGua (8-oxo-7,8-dihydroguanine) is produced in nucleic acids as well as in nucleotide pools of cells, by reactive oxygen species normally formed during cellular metabolic processes. MutT protein of Escherichia coli specifically degrades 8-oxoGua-containing deoxyribo- and ribonucleoside triphosphates to corresponding nucleoside monophosphates, thereby preventing misincorporation of 8-oxoGua into DNA and RNA, which would cause mutation and phenotypic suppression, respectively. Here, we report that the MutT protein has additional activities for cleaning up the nucleotide pools to ensure accurate DNA replication and transcription. It hydrolyzes 8-oxo-dGDP to 8-oxo-dGMP with a K(m) of 0.058 microM, a value considerably lower than that for its normal counterpart, dGDP (170 microM). Furthermore, the MutT possesses an activity to degrade 8-oxo-GDP to the related nucleoside monophosphate, with a K(m) value 8000 times lower than that for GDP. These multiple enzyme activities of the MutT protein would facilitate the high fidelity of DNA and RNA syntheses.

Topics: Deoxyadenine Nucleotides; Deoxycytosine Nucleotides; Deoxyguanine Nucleotides; DNA Replication; DNA, Bacterial; Escherichia coli Proteins; Guanine; Guanosine Triphosphate; Hydrolysis; Kinetics; Multienzyme Complexes; Phosphoric Monoester Hydrolases; Pyrophosphatases; RNA, Bacterial; Thymine Nucleotides; Transcription, Genetic