Monomeric Cu,Zn-superoxide Dismutase Is a Common Misfolding Intermediate in the Oxidation Models of Sporadic and Familial Amyotrophic Lateral Sclerosis

Rishi Rakhit,John P Crow,James R Lepock,Leslie H Kondejewski,Neil R Cashman,Avijit Chakrabartty

doi:10.1074/jbc.m313295200

Abstract

Proteinacious intracellular aggregates in motor neurons are a key feature of both sporadic and familial amyotrophic lateral sclerosis (ALS). These inclusion bodies are often immunoreactive for Cu,Zn-superoxide dismutase (SOD1) and are implicated in the pathology of ALS. On the basis of this and a similar clinical presentation of symptoms in the familial (fALS) and sporadic forms of ALS, we sought to investigate the possibility that there exists a common disease-related aggregation pathway for fALS-associated mutant SODs and wild type SOD1. We have previously shown that oxidation of fALS-associated mutant SODs produces aggregates that have the same morphological, structural, and tinctorial features as those found in SOD1 inclusion bodies in ALS. Here, we show that oxidative damage of wild type SOD at physiological concentrations ( approximately 40 microm) results in destabilization and aggregation in vitro. Oxidation of either mutant or wild type SOD1 causes the enzyme to dissociate to monomers prior to aggregation. Only small changes in secondary and tertiary structure are associated with monomer formation. These results indicate a common aggregation prone monomeric intermediate for wild type and fALS-associated mutant SODs and provides a link between sporadic and familial ALS.

Highlights

Proteinacious intracellular aggregates in motor neurons are a key feature of both sporadic and familial amyotrophic lateral sclerosis (ALS)
We have previously shown that oxidation of fALS-associated mutant SODs produces aggregates that have the same morphological, structural, and tinctorial features as those found in SOD1 inclusion bodies in ALS
We have found that oxidation of holo-wild type SOD1 at concentrations that have been reported in human brain results in its aggregation in vitro

Summary

Introduction

Proteinacious intracellular aggregates in motor neurons are a key feature of both sporadic and familial amyotrophic lateral sclerosis (ALS). Small changes in secondary and tertiary structure are associated with monomer formation These results indicate a common aggregation prone monomeric intermediate for wild type and fALS-associated mutant SODs and provides a link between sporadic and familial ALS. One hypothesis of the gain of function of SOD1 is that misfolding of the mutant alters the catalytic mechanism to allow production of oxidants such as peroxynitrite [4] and possibly hydrogen peroxide [5] These reactive nitrogen and oxygen species cause toxicity by accumulated damage to proteins, nucleic acids, and lipids. SOD1 inclusion bodies, which react with anti-ubiquitin antibodies, are a common pathological finding in motor neurons and neighboring astrocytes of ALS patients [6] These two hypotheses, are not mutually exclusive when considering that oxidative modification of proteins may contribute to aggregation and protease resistance. We used the same model to dissect the kinetics of the SOD1 aggregation pathway

Methods

Results

Conclusion