The ALS-Associated Mutation G93A in Human Copper-Zinc Superoxide Dismutase Selectively Destabilizes the Remote Metal Binding Region

Abstract

More than 100 distinct mutations in the gene (SOD1) for human copper-zinc superoxide dismutase (CuZnSOD) have been associated with familial amyotrophic lateral sclerosis (fALS). Studies of these mutant proteins, which often have been performed under far from physiological conditions, have indicated effects on protein stabilities, catalytic activity, and metal binding affinities but with no common pattern. Also, with the knowledge that ALS is a late onset disease it is apparent that protein interactions which contribute to the disorder might, in the natural cellular milieu, depend on a delicate balance between intrinsic protein properties. In this study, we have used experimental conditions as near as possible to the in vivo conditions to reduce artifacts emanating from the experimental setup. Using 1H-15N HSQC NMR spectroscopy, we have analyzed hydrogen exchange at the amide groups of wild-type (wt) CuZnSOD and the fALS-associated G93A SOD variant in their fully metalated states. From analyses of the exchange pattern, we have characterized the local dynamics at 64% of all positions in detail in both the wt and G93A protein. The results show that the G93A mutation had no effect on the dynamics at a majority of the investigated positions. However, the mutation results in local destabilization at the site of the mutation and also in stabilization at a few positions that were apparently scattered over the entire protein surface. Most remarkably, the mutation selectively destabilized the remote metal binding region. The results indicate that the metal binding region may affect the intermolecular protein-protein interactions which cause formation of protein aggregates.