The effect of aging on post-translational modifications of wild-type human SOD1 and the A5V ALS mutant

Cu/Zn superoxide dismutase 1 (SOD1) is essential for maintaining neural health. Its functions include modulating metabolism, maintaining redox balance, regulating transcription, besides eliminating superoxide radicals, which are achieved through various post-translational modifications (PTMs). Consequently, unusual PTMs in SOD1 can impair its functionality and stability, leading to the accumulation of misfolded SOD1 and the increase of oxidative stress markers, hallmarks of Amyotrophic Lateral Sclerosis (ALS). Although SOD1 has been extensively studied, especially regarding its role in ALS, relatively little is known about how aging and mutations affect SOD1 PTMs. This study aimed to evaluate the effect of oxidative stress induced by chronological aging on PTMs of human SOD1: wild-type (WT) and A5V SOD1, a severe ALS-related mutant. To do this, both hSOD1 forms were expressed in Saccharomyces cerevisiae lacking the SOD1 gene, and then purified from extracts of stressed and non-stressed cells. PTMs were analyzed using mass spectrometry, observing the modification of WT and mutant human SOD1 in both conditions. We observed changes in the levels of damage, including oxidation, formylation, and carboxylation, such as oxidized tryptophan 33, associated with prion-like propagation of SOD1 misfolding. Increased levels of this PTM appeared in WT SOD1 after aging and in A5V SOD1. Acetylation and succinylation were also found on lysines. Some of these modifications already have described functions in the literature, while others still lack a defined role. Interestingly, the levels of these physiological PTMs differed between WT and mutant SOD1, providing important information for elucidating the molecular mechanisms of ALS involving SOD1.