DNA glycosylases for 8-oxoguanine repair in Staphylococcus aureus

A non-canonical nucleotide from viral genomes interferes with the oxidative DNA damage repair system

Oxidative damage is a major source of genomic instability in all organisms with the aerobic metabolism. 8-Oxoguanine (8-oxoG), an abundant oxidized purine, is mutagenic and must be controlled by a dedicated DNA repair system (GO system) that prevents G:C→T:A transversions through an easily formed 8-oxoG:A mispair. In some forms, the GO system is present in nearly all cellular organisms. However, recent studies uncovered many instances of viruses possessing non-canonical nucleotides in their genomes. The features of genome damage and maintenance in such cases of alternative genetic chemistry remain barely explored. In particular, 2,6-diaminopurine (Z nucleotide) completely substitutes for A in the genomes of some bacteriophages, which have evolved pathways for dZTP synthesis and specialized polymerases that prefer dZTP over dATP. Here we address the ability of the GO system enzymes to cope with oxidative DNA damage in the presence of Z in DNA. DNA polymerases of two different structural families (Klenow fragment and RB69 polymerase) were able to incorporate dZMP opposite to 8-oxoG in the template, as well as 8-oxodGMP opposite to Z in the template. Fpg, a 8-oxoguanine-DNA glycosylase that discriminates against 8-oxoG:A mispairs, also did not remove 8-oxoG from 8-oxoG:Z mispairs. However, MutY, a DNA glycosylase that excises A from pairs with 8-oxoG, had a significantly lower activity on Z:8-oxoG mispairs. Similar preferences were observed for Fpg and MutY from different bacterial species (Escherichia coli, Staphylococcus aureus and Lactococcus lactis). Overall, the relaxed control of 8-oxoG in the presence of the Z nucleotide may be a source of additional mutagenesis in the genomes of bacteriophages or bacteria that have survived the viral invasion.

The contribution of DNA repair pathways to Staphylococcus aureus fitness and fidelity during nitric oxide stress

Staphylococcus aureus is a major human pathogen that causes a variety of illnesses, ranging from minor skin and soft tissue infections to more severe systemic infections. Although the primary host immune response can typically clear bacterial infections, S. aureus is uniquely resistant to inflammation. For instance, our laboratory has determined that S. aureus is highly resistant to nitric oxide (NO⋅), an important component of the innate immune response that plays a role in both immunomodulatory and antibacterial processes. Additionally, NO⋅ and its derivatives can cause damage to S. aureus DNA, more specifically, deamination and/or oxidation of DNA bases; however, regulation and repair mechanisms of DNA in S. aureus are understudied. Thus, we hypothesize that several DNA repair mechanisms may account for the replication fidelity of S. aureus and may contribute to fitness in the presence of NO⋅. Here, we show the role of several DNA repair mechanisms in S. aureus. More specifically, we found that recombinational repair genes recJ, recG, and polA may play a role in the repair of NO⋅-induced replication fork collapses. We also show the role of the base excision repair pathway protein, MutY, in reducing NO⋅-mediated mutagenesis. Overall, our results suggest that NO⋅ leads to DNA damage, which subsequently induces the activity of several DNA repair pathways, contributing to the replication fidelity and fitness of S. aureus.IMPORTANCEPathogenic bacteria must evolve various mechanisms in order to evade the host immune response that they are infecting. One aspect of the primary host immune response to an infection is the production of an inflammatory effector component, nitric oxide (NO⋅). Staphylococcus aureus has uniquely evolved a diverse array of strategies to circumvent the inhibitory activity of nitric oxide. One such mechanism by which S. aureus has evolved allows the pathogen to survive and maintain its genomic integrity in this environment. For instance, here, our results suggest that S. aureus employs several DNA repair pathways to ensure replicative fitness and fidelity under NO⋅ stress. Thus, our study presents evidence of an additional strategy that allows S. aureus to evade the cytotoxic effects of host NO⋅.

OGG1 in the Kidney: Beyond Base Excision Repair

8-Oxoguanine DNA glycosylase (OGG1) is a repair protein for 8-oxoguanine (8-oxoG) in eukaryotic atopic DNA. Through the initial base excision repair (BER) pathway, 8-oxoG is recognized and excised, and subsequently, other proteins are recruited to complete the repair. OGG1 is primarily located in the cytoplasm and can enter the nucleus and mitochondria to repair damaged DNA or to exert epigenetic regulation of gene transcription. OGG1 is involved in a wide range of physiological processes, such as DNA repair, oxidative stress, inflammation, fibrosis, and autophagy. In recent years, studies have found that OGG1 plays an important role in the progression of kidney diseases through repairing DNA, inducing inflammation, regulating autophagy and other transcriptional regulation, and governing protein interactions and functions during disease and injury. In particular, the epigenetic effects of OGG1 in kidney disease have gradually attracted widespread attention. This study reviews the structure and biological functions of OGG1 and the regulatory mechanism of OGG1 in kidney disease. In addition, the possibility of OGG1 as a potential therapeutic target in kidney disease is discussed.

DNA Repair in Staphylococcus aureus

Staphylococcus aureus is a common cause of both superficial and invasive infections of humans and animals. Despite a potent host response and apparently appropriate antibiotic therapy, staphylococcal infections frequently become chronic or recurrent, demonstrating a remarkable ability of S. aureus to withstand the hostile host environment. There is growing evidence that staphylococcal DNA repair makes important contributions to the survival of the pathogen in host tissues, as well as promoting the emergence of mutants that resist host defenses and antibiotics. While much of what we know about DNA repair in S. aureus is inferred from studies with model organisms, the roles of specific repair mechanisms in infection are becoming clear and differences with Bacillus subtilis and Escherichia coli have been identified. Furthermore, there is growing interest in staphylococcal DNA repair as a target for novel therapeutics that sensitize the pathogen to host defenses and antibiotics. In this review, we discuss what is known about staphylococcal DNA repair and its role in infection, examine how repair in S. aureus is similar to, or differs from, repair in well-characterized model organisms, and assess the potential of staphylococcal DNA repair as a novel therapeutic target.