Mechanisms for the repair of oxidative stress-induced DNA damage in Porphyromonas

牙龈卟啉单胞菌作为一种“关键病原体”，突出了其适应严酷炎症的能力

Porphyromonas gingivalis, as a “keystone pathogen”, highlights its ability to adapt to the harsh inflammatory conditions of the periodontal pocket. Because the environmental stress response is a major determinant of its virulence, it is our long-term goal to gain a comprehensive understanding of its survival strategy(s). DNA damage is a major consequence of oxidative stress. While more than 20 different oxidatively altered bases might be generated by this stress, 8-oxo-7,8-dihydroguanine (8-oxoG) is one of the most common product of DNA damage. Guanine is the most susceptible base to oxidation and forms mainly 8-oxoG due to its low redox potential. In prokaryotic cells the presence of 8-oxoG is mainly repaired by base excision repair (BER). A survey of the P. gingivalis genome indicate that an important component of the BER system is missing. Because the average G + C content of the genome of P. gingivalis is 49%, a mechanism(s) to prevent or repair lesions resulting from guanine oxidation is vital. There is a gap in our comprehensive knowledge on a mechanism(s) for the repair of oxidative stress-induced DNA damage in P. gingivalis. We have previously demonstrated that there is an accumulation of 8-oxoG in the chromosome of P. gingivalis exposed to H2O2-induced oxidative stress. Neither BER nor nucleotide excision repair (NER), as observed in other strains, appear to be involved in the repair of the 8-oxoG lesion in P. gingivalis. DNA affinity fractionation identified PG1037, a conserved hypothetical protein, among others, that were preferentially bound to the oligonucleotide fragment carrying the 8-oxo-G lesion. PG1037 is part of the uvrA-pg1037-pcrA operon in P. gingivalis which is known to be upregulated under H2O2- induced stress. The purified recombinant PG1037 protein, likely via a reducing function, has the ability to prevent Fenton chemistry-mediated DNA damage in vitro and, under oxidative stress conditions, reduced the cleavage of the 8-oxoG lesion by the E.coli foramidopyrimidine glycosylase (Fpg) enzyme. In silico analysis of PG1037 shows a protein that contains a zinc finger domain, two peroxidase homologous motifs and a cytidylate kinase domain. The goal of the proposal is to test the hypothesis that a novel P. gingivalis protein (PG1037) carrying peroxidase motifs and a zinc finger domain is involved in the repair of oxidatively damaged DNA. Our aims are to confirm the specific role of PG1037 in the removal of 8-oxoG from duplex DNA and to evaluate any interaction of PG1037 with other proteins in that process. The data will provide a major conceptual advance on the molecular bases for the repair of oxidative stress-induced DNA damage in P. gingivalis and could likely support a unique and effective DNA repair mechanism we propose to designate “base redox repair”. It will set the stage, in a future RO1 application, to address specific structure-function questions on the vital components and their corporation in maintaining genomic stability in anaerobes exposed to environmental stress. These components could be targets for the development of novel therapeutic interventions for the control and prevention of P. gingivalis-associated diseases.