Discovery and properties of a monoclonal antibody targeting 8-oxoA, an oxidized adenine lesion in DNA and RNA

Deprotonation of 8-Oxo-7,8-dihydroadenine Radical Cation in Free and Encumbered Context: A Theoretical Study

Due to the lower oxidation potential than natural nucleic acid bases, one-electron oxidation of DNA is usually funneled into the direction of intermediates for oxidized DNA damage like 8-oxo-7,8-dihydroadenine (8-oxoA) leading to a radical cation, which may undergo facile deprotonation. However, compared to the sophisticated studies devoted to natural bases, much less is known about the radical cation degradation behavior of an oxidized DNA base. Inspired by this, a comprehensive theoretical investigation is performed to illuminate the deprotonation of 8-oxoA radical cation (8-oxoA•+) in both free and encumbered context by calculating the pK a value and mapping the energy profiles. The calculative pK a values of active protons in free 8-oxoA•+ follow the order: N7-H < N9-H < N6-H1< N6-H2, suggesting the preference of proton departure in free 8-oxoA•+. To further illustrate the preferred site and mechanism for 8-oxoA•+ deprotonation, energy profiles are constructed to distinguish the possibility from that of all active protons in both contexts. The results show distinctly that 8-oxoA•+ mainly suffers from the loss of proton from N9 due to the lowest energy barrier but deprotonates N7-H in real DNA as the connection of N9 and ribose. The energy barriers for the deprotonation of N7-H from 8-oxoA•+ in free and encumbered contexts are 1.5 and 1.3 kcal/mol, respectively, indicating a fast deprotonation reaction. It is more interestingly that the N9-H proton transfer (PT, toward N3) to adjacent water follows a stepwise fashion rather than a one-step approach as previously reported. Furthermore, the PT behavior of free N9-H toward O8 is dramatically influenced by base pairing T, where it is localized at neighboring water without further PT to adjacent water in free 8-oxoA•+ but migrated directly to adjacent water in the 8-oxoA•+:T base pair. And the deprotonation of N6-H2 in 8-oxoA•+:T is disturbed as the PT to O4 of the pairing T base is inhibited. It is warmly anticipated that these results could provide an in-depth perspective to understand the important role of 8-oxoA in mutation.

Mapping the future of oxidative RNA damage in neurodegeneration: Rethinking the status quo with new tools

Over two decades ago, increased levels of RNA oxidation were reported in postmortem patients with ALS, Alzheimer's, Parkinson's, and other neurodegenerative diseases. Interestingly, not all cell types and transcripts were equally oxidized. Furthermore, it was shown that RNA oxidation is an early phenomenon, altogether indicating that oxidative RNA damage could be a driver, and not a consequence, of disease. Despite all these exciting observations, the field appears to have stagnated since then. We argue that this is a consequence of the shortcomings of technologies to model these diseases, limiting our understanding of which transcripts are being oxidized, which RNA-binding proteins are interacting with these RNAs, what their implications are in RNA processing, and as a result, what their potential role is in disease onset and progression. Here, we discuss the limits of previous technologies and propose ways by which advancements in iPSC-derived disease modeling, proteomics, and sequencing technologies can be combined and leveraged to answer new and decades-old questions.

Selective 8-oxo-rG stalling occurs in the catalytic core of polynucleotide phosphorylase (PNPase) during degradation

RNA oxidation, predominantly through the accumulation of 8-oxo-7,8-dihydroguanosine (8-oxo-rG), represents an important biomarker for cellular oxidative stress. Polynucleotide phosphorylase (PNPase) is a 3'-5' exoribonuclease that has been shown to preferentially recognize 8-oxo-rG-containing RNA and protect Escherichia coli cells from oxidative stress. However, the impact of 8-oxo-rG on PNPase-mediated RNA degradation has not been studied. Here, we show that the presence of 8-oxo-rG in RNA leads to catalytic stalling of E. coli PNPase through in vitro RNA degradation experiments and electrophoretic analysis. We also link this stalling to the active site of the enzyme through resolution of single-particle cryo-EM structures for PNPase in complex with singly or doubly oxidized RNA oligonucleotides. Following identification of Arg399 as a key residue in recognition of both single and sequential 8-oxo-rG nucleotides, we perform follow-up in vitro analysis to confirm the importance of this residue in 8-oxo-rG-specific PNPase stalling. Finally, we investigate the effects of mutations to active site residues implicated in 8-oxo-rG binding through E. coli cell growth experiments under H2O2-induced oxidative stress. Specifically, Arg399 mutations show significant effects on cell growth under oxidative stress. Overall, we demonstrate that 8-oxo-rG-specific stalling of PNPase is relevant to bacterial survival under oxidative stress and speculate that this enzyme might associate with other cellular factors to mediate this stress.

The role of DNA and RNA guanosine oxidation in cardiovascular diseases

Cardiovascular diseases (CVD) persist as a prominent cause of mortality worldwide, with oxidative stress constituting a pivotal contributory element. The oxidative modification of guanosine, specifically 8-oxoguanine, has emerged as a crucial biomarker for oxidative stress, providing novel insights into the molecular underpinnings of CVD. 8-Oxoguanine can be directly generated at the DNA (8-oxo-dG) and RNA (8-oxo-G) levels, as well as at the free nucleotide level (8-oxo-dGTP or 8-oxo-GTP), which are produced and can be integrated through DNA replication or RNA transcription. When exposed to oxidative stress, guanine is more readily produced in RNA than in DNA. A burgeoning body of research surrounds 8-oxoguanine, exhibits its accumulation playing a pivotal role in the development of CVD. Therapeutic approaches targeting oxidative 8-Oxoguanine damage to DNA and RNA, encompassing the modulation of repair enzymes and the development of small molecule inhibitors, are anticipated to enhance CVD management. In conclusion, we explore the noteworthy elevation of 8-oxoguanine levels in patients with various cardiac conditions and deliberate upon the formation and regulation of 8-oxo-dG and 8-oxo-G under oxidative stress, as well as their function in CVD.