Impact of G-quadruplex RNA oxidation on its conformational dynamics and interaction with ALS-associated TDP-43.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the selective degeneration of motor neurons. The primary cause of ALS, whether sporadic or familial, is aging, and recent studies have shown that age-related RNA oxidation plays a role in the early stages of disease onset. This study focused on the vulnerability of G-quadruplex (G4) structures to oxidation and aimed to elucidate the molecular mechanism underlying the conformational changes and their interactions with the binding protein TDP-43. Guanine within G4 structures has a low redox potential, and its substitution with 8-oxoguanine (8OG) can induce structural instability and impair its function as a protein binding signal. In addition, synthetic G4-RNAs modified by oxidation were examined, and results showed that conformational changes are due to different hydrogen bond arrangements, 8OG-A mismatches, and intermolecular G4 formation. The interaction between G4 and TDP-43 decreased in proportion to the substitution rate of 8OG. Furthermore, ALS-associated mutant proteins exhibited reduced binding affinity for oxidized G4s compared with the wild-type. Considering that intra-axonal mRNA transport mediated by G4-binding proteins is essential for the survival and activity of motor neurons, this study will provide important insights into the molecular mechanisms underlying the onset of ALS with aging.