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Mutations in SOD1 associated with amyotrophic lateral sclerosis cause novel protein interactions
C B Kunst1, E Mezey, M J Brownstein
1Eleanor Roosevelt Institute for Cancer Research, Denver, Colorado, USA.
Abstract:
A subset of familial and sporadic amyotrophic lateral sclerosis (ALS-a fatal disorder characterised by progressive motor neuron degeneration) cases are due to mutations in the gene encoding Cu,Zn superoxide dismutase (SOD1). Two mutations which have been successfully used to generate transgenic mice that develop an ALS-like syndrome are glycine 85 to arginine (G85R) and glycine 93 to alanine (G93A) with the mutant SOD1 allele overexpressed in a normal mouse genetic background. No ALS-like phenotype is observed in mice overexpressing wild-type SOD1 or mice without any SOD1 activity. These dominant mutations, which do not necessarily decrease SOD1 activity, may confer a gain of function that is selectively lethal to motor neurons. The yeast interaction trap system allowed us to determine whether these mutations in SOD1 caused novel protein interactions not observed with wild-type SOD1 and which might participate in the generation of the ALS phenotype. Two proteins, lysyl-tRNA synthetase and translocon-associated protein delta, interact with mutant forms of SOD1 but not with wild-type SOD1. The specificity of the interactions was confirmed by the coimmunoprecipitation of mutant SOD1 and the expressed proteins. These proteins are expressed in ventral cord, lending support to the relevance of this interaction to motor neuron disease.
Insights
Mutant copper-zinc superoxide dismutase (SOD1) proteins interact with novel partners, leading to motor neuron death in amyotrophic lateral sclerosis (ALS). This gain-of-function mechanism explains SOD1-linked ALS pathogenesis.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease.
- Mutations in the Cu,Zn superoxide dismutase (SOD1) gene cause a subset of familial and sporadic ALS cases.
- Specific SOD1 mutations (G85R, G93A) in transgenic mice induce an ALS-like syndrome.
Purpose of the Study:
- To investigate novel protein interactions of mutant SOD1.
- To determine if these interactions contribute to the motor neuron degeneration observed in ALS.
- To explore the gain-of-function mechanism in SOD1-linked ALS.
Main Methods:
- Utilized the yeast interaction trap system to screen for SOD1-interacting proteins.
- Employed coimmunoprecipitation to confirm protein interactions.
- Analyzed protein expression in mouse ventral cord tissue.
Main Results:
- Identified two novel proteins, lysyl-tRNA synthetase and translocon-associated protein delta, that interact specifically with mutant SOD1.
- Confirmed these interactions are not observed with wild-type SOD1.
- Detected expression of these interacting proteins in the ventral cord, relevant to motor neuron disease.
Conclusions:
- Mutant SOD1 gains novel protein interactions, suggesting a gain-of-function mechanism in ALS pathogenesis.
- These specific interactions may be critical for the selective toxicity of motor neurons in SOD1-linked ALS.
- Further research into these interactions could reveal therapeutic targets for ALS.