| Over 100 mutations in the protein human Cu/Zn superoxide dismutase 1 (SOD) have been identified as a causal factor in some familial and sporadic forms of amyotrophic lateral sclerosis (Lou Gehrig's Disease). As of yet, it is unclear what the toxic mechanism underlying the pathology of ALS is and how the different mutations in SOD cause the toxicity leading to the same disease pathology. It has been suggested that increased aggregation propensities of the mutated proteins are responsible for the ALS-pathologies, but little is known about what the toxic aggregates are, how they form, and how they become selectively toxic to motor neurons. Hence, we hypothesized that aggregated SOD might behave similar to those from amyloidogenic proteins found in other neurodegenerative diseases.;In this thesis, successful experimental evidence of different apo SOD-aggregating conditions leading to fibril and pore structures that are characteristic of amyloidogenic proteins is shown. Furthermore, the structurally distinct aggregates that were formed under different conditions appear to involve a common precursor conformer (open dimer) that can be uniquely characterized apart from the known native dimeric structure of wild-type SOD. Experimentation through various biochemical and biophysical studies suggest critical roles of “open” dimers in the process of apo SOD aggregation. Based on the experimental results, we propose a mechanism of SOD aggregation that can be used to explain various observations made in the clinical and model studies of SOD-mediated ALS. In addition, we have computationally identified orotic acid as a potential binding ligand to the cysteine 111 crevice of SOD with the ability to inhibit the aggregation according to our proposed aggregation mechanism. Under oxidative aggregation condition, 0.1 mM orotate blocks the aggregation of both WT and pathogenic mutant SOD. This successful implementation of our aggregation mechanism in computational design of anti-aggregation ligand provides a hope for future designs of candidate drug molecules that may be used to treat ALS. |
