Mutations in copper-zinc superoxide dismutase that cause amyotrophic lateral sclerosis alter the zinc binding site and the redox behavior of the protein.

Abstract

A series of mutant human and yeast copperzinc superoxide dismutases has been prepared, with mutations corresponding to those found in familial amyotrophic lateral sclerosis (ALS; also known as Lou Gehrig's disease). These proteins have been characterized with respect to their metal-binding characteristics and their redox reactivities. Replacement of Zn2+ ion in the zinc sites of several of these proteins with either Cu2+ or Co2+ gave metal-substituted derivatives with spectroscopic properties different from those of the analogous derivative of the wild-type proteins, indicating that the geometries of binding of these metal ions to the zinc site were affected by the mutations. Several of the ALS-associated mutant copper-zinc superoxide dismutases were also found to be reduced by ascorbate at significantly greater rate than the wild-type proteins. We conclude that similar alterations in the properties of the zinc binding site can be caused by mutations scattered throughout the protein structure. This finding may help to explain what is perhaps the most perplexing question in copper-zinc superoxide dismutase-associated familial ALS-i.e., how such a diverse set of mutations can result in the same gain of function that causes the disease.

The proportion of mutations predicted to have a deleterious effect differs between gain and loss of function genes in neurodegenerative disease

“…Complementation assays in yeast and insect cell lines have identified several SOD1 mutations that retain nearwildtype dismutase enzymatic activity for SOD1, while others that affect metal-binding regions result in as little as 1% of enzymatic activity Lyons, et al, 1996;Valentine, et al, 2005). In total, 28 mutations that were examined displayed wildtype-like properties (normal enzymatic activity) and 8 affected metal binding.…”

Oxidation-induced Misfolding and Aggregation of Superoxide Dismutase and Its Implications for Amyotrophic Lateral Sclerosis

“…One property shared by many FALS-associated SOD1 mutants is a decreased affinity for Zn 2ϩ (8,9). It has been proposed that reduced Zn 2ϩ binding destabilizes the structure of SOD1, increasing the rate of abnormal reduction of bound Cu 2ϩ to Cu ϩ by intracellular reducing agents.…”

The Disulfide Bond, but Not Zinc or Dimerization, Controls Initiation and Seeded Growth in Amyotrophic Lateral Sclerosis-linked Cu,Zn Superoxide Dismutase (SOD1) Fibrillation

“…Some of these conditions, notably low pH, elevated temperatures, trifluoroethanol, and incubation in reducing agents, generate aggregates that bear a remarkable resemblance to amyloid fibrils. Unfortunately conditions such as low pH or elevated temperatures are likely to lead to scrambling or loss of bound metals in partially metallated SOD1 and can lead to dimer dissociation (25)(26)(27). Such methods are therefore unsuitable for studies of partially metallated forms of SOD.…”