Tryptophan 32 Potentiates Aggregation and Cytotoxicity of a Copper/Zinc Superoxide Dismutase Mutant Associated with Familial Amyotrophic Lateral Sclerosis

David M Taylor,Bernard F Gibbs,Edor Kabashi,Sandra Minotti,Heather D Durham,Jeffrey N Agar

doi:10.1074/jbc.m610119200

Abstract

One familial form of the neurodegenerative disease, amyotrophic lateral sclerosis, is caused by gain-of-function mutations in the gene encoding copper/zinc superoxide dismutase (SOD-1). This study provides in vivo evidence that normally occurring oxidative modification to SOD-1 promotes aggregation and toxicity of mutant proteins. The oxidation of Trp-32 was identified as a normal modification being present in both wild-type enzyme and SOD-1 with the disease-causing mutation, G93A, isolated from erythrocytes. Mutating Trp-32 to a residue with a slower rate of oxidative modification, phenylalanine, decreased both the cytotoxicity of mutant SOD-1 and its propensity to form cytoplasmic inclusions in motor neurons of dissociated mouse spinal cord cultures.

Highlights

Amyotrophic lateral sclerosis (ALS)5 is an adult onset neurodegenerative disease in which two percent of all cases are caused by mutations in the gene encoding copper/zinc superoxide dismutase (SOD-1) [1]
Mass Spectral Evidence for Oxidation of Tryptophan 32 (Trp-32) in As-isolated SOD-1—Using immunoaffinity chromatography with antibodies raised against partially oxidized human SOD-1wt, SOD-1 was purified from human blood, and SOD-1wt and SOD-1G93A were purified from transgenic mouse blood
The results presented indicate that oxidation of Trp-32 occurs in vivo as a natural modification to SOD-1 and that the Trp-32 residue is an important mediator of the toxicity of an SOD-1G93A mutant associated with familial ALS (fALS)

Summary

Introduction

Amyotrophic lateral sclerosis (ALS)5 is an adult onset neurodegenerative disease in which two percent of all cases are caused by mutations in the gene encoding copper/zinc superoxide dismutase (SOD-1) [1]. This study provides in vivo evidence that normally occurring oxidative modification to SOD-1 promotes aggregation and toxicity of mutant proteins. The oxidation of Trp-32 was identified as a normal modification being present in both wild-type enzyme and SOD-1 with the disease-causing mutation, G93A, isolated from erythrocytes.

Results

Conclusion