DNA-Accelerated Aggregation Of Oxidation-Induced Modification Of Copper, Zinc Superoxide Dismutase Under Physiological Conditions

Amyotrophic lateral sclerosis (ALS) is one of the most common adult neurodegenerative diseases with unknown causes. The structural and the metal-binding variations in Cu Zn superoxide dismutase (SOD1) mutants have been linked to many kinds of neurodegenerative diseases, in particular, amyotrophic lateral sclerosis, due to their oxidative damage and aggregation. It is well known that oxidation-induced modification of SOD1 can be used to mimic SOD1 mutants in vitro under physiological conditions. The aggregation behavior of SOD1 were examined under oxidative conditions, which could mimic the effect of mutations and reflect the practical process done under physiological conditions to a high extent.The present study examined the oxidation-induced modification of SOD1 in the presence of ascorbate and DNA can be used to accelerate the formation of SOD1 aggregates by a series of biochemical experiments.The oxidation-induced modification of SOD1 were tested by SDS-PAGE and 2-D electrophoresis. The results reveal that the pI and the hydrophobicity of oxidative SOD1 are increased. Two forms of DNA were tested to trigger the oxidative SOD1 aggregation by light scattering and direct observations under visible light, the one form of DNA is double-stranded DNA (dsDNA), the other form of DNA is single-stranded DNA (ssDNA). The results reveal that dsDNA acts as a template for accelerating the formation of SOD1 aggregates and is incorporated into SOD1 aggregates. A significant alteration in the pI and the hydrophobicity of SOD1 caused by oxidation, and the enrichment in SOD1 along dsDNA double strands are two main reasons responsible for DNA-accelerated SOD1 aggregation.The acceleration effect of SOD1 aggregation in vitro upon addition of ssDNA of 24 nucleotides was examined under physiological conditions. ssDNA was tested to trigger the SOD1 aggregation by light scattering and direct observations under visible light. The results reveal that ssDNA can accelerate the formation of ssDNA-SOD1 aggregate monomer, oligomeric aggregate, microaggregate, and macroaggregate. All these results indicate that the ssDNA-accelerated formation of insoluble SOD1 aggregates can act as a potential pathway to avoid accumulation of soluble SOD1 oligomeric intermediates. The small DNAs that are easily synthesized to target at protein oligomers might lower pathological consequences of SOD1.