MTH1 is an enzyme that hydrolyzes 8-oxo-dGTP, which is an oxidatively damaged nucleobase, into 8-oxo-dGMP in nucleotide pools to prevent its mis-incorporation into genomic DNA. Selective and potent MTH1-binding molecules have potential as biological tools and drug candidates. We recently developed 8-halogenated 7-deaza-dGTP as an 8-oxo-dGTP mimic and found that it was not hydrolyzed, but inhibited enzyme activity. To further increase MTH1 binding, we herein designed and synthesized 7,8-dihalogenated 7-deaza-dG derivatives. We successfully synthesized multiple derivatives, including substituted nucleosides and nucleotides, using 7-deaza-dG as a starting material. Evaluations of the inhibition of MTH1 activity revealed the strong inhibitory effects on enzyme activity of the 7,8-dihalogenated 7-deaza-dG derivatives, particularly 7,8-dibromo 7-daza-dGTP. Based on the results obtained on kinetic parameters and from computational docking simulating studies, these nucleotide analogs interacted with the active site of MTH1 and competitively inhibited the substrate 8-oxodGTP. Therefore, novel properties of repair enzymes in cells may be elucidated using new compounds.
8-OxodGTP is generated by the reaction between dGTP and reactive oxygen species and a considered mutagenic nucleotide. It can be incorporated into the duplex DNA during replication processes by the DNA polymerase, and thus the repair enzyme removes oxodGTP from the nucleotide pools in living cells. On the other hand, the γ-modified triphosphates show interesting properties for use as biological tools. Therefore, the γ-N-pyrenylalkyl-oxodGTP derivatives were synthesized and their effect on the enzymatic reactions were evaluated. The γ-N-pyrenylmethyl-oxodGTP was found to be accepted by the DNA polymerase just like oxodGTP, but showed a competitive inhibition property for the human oxodGTPase.
Freshwater ecosystems are highly biodiverse1 and important for livelihoods and economic development2, but are under substantial stress3. To date, comprehensive global assessments of extinction risk have not included any speciose groups primarily living in freshwaters. Consequently, data from predominantly terrestrial tetrapods4,5 are used to guide environmental policy6 and conservation prioritization7, whereas recent proposals for target setting in freshwaters use abiotic factors8-13. However, there is evidence14-17 that such data are insufficient to represent the needs of freshwater species and achieve biodiversity goals18,19. Here we present the results of a multi-taxon global freshwater fauna assessment for The IUCN Red List of Threatened Species covering 23,496 decapod crustaceans, fishes and odonates, finding that one-quarter are threatened with extinction. Prevalent threats include pollution, dams and water extraction, agriculture and invasive species, with overharvesting also driving extinctions. We also examined the degree of surrogacy of both threatened tetrapods and freshwater abiotic factors (water stress and nitrogen) for threatened freshwater species. Threatened tetrapods are good surrogates when prioritizing sites to maximize rarity-weighted richness, but poorer when prioritizing based on the most range-restricted species. However, they are much better surrogates than abiotic factors, which perform worse than random. Thus, although global priority regions identified for tetrapod conservation are broadly reflective of those for freshwater faunas, given differences in key threats and habitats, meeting the needs of tetrapods cannot be assumed sufficient to conserve freshwater species at local scales.