Title

Disulfide-Reduced ALS Variants of Cu, Zn Superoxide Dismutase Exhibit Increased Populations of Unfolded Species.

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Publication Date

2010-02-22

Document Type

Article

Subjects

Amyotrophic Lateral Sclerosis; Disulfides; Superoxide Dismutase; Protein Folding; Cell Aggregation

Disciplines

Biochemistry, Biophysics, and Structural Biology | Pharmacology, Toxicology and Environmental Health

Abstract

Cu, Zn superoxide dismutase (SOD1) is a dimeric metal binding enzyme responsible for the dismutation of toxic superoxide to hydrogen peroxide and oxygen in cells. Mutations at dozens of sites in SOD1 induce amyotrophic lateral sclerosis (ALS), a fatal gain-of-function neurodegenerative disease whose molecular basis is unknown. To obtain insights into effects of the mutations on the folded and unfolded populations of immature monomeric forms whose aggregation or self-association may be responsible for ALS, the thermodynamic and kinetic folding properties of a set of disulfide-reduced and disulfide-oxidized Zn-free and Zn-bound stable monomeric SOD1 variants were compared to the wild-type (WT) protein. The most striking effect of the mutations on the monomer stability was observed for the disulfide-reduced metal-free variants. Whereas the WT and S134N monomers are >95% folded at neutral pH and 37 degrees C, A4V, L38V, G93A, and L106V ranged from 50% to ~90% unfolded. The reduction of the disulfide-bond was also found to reduce the apparent Zn affinity of the WT monomer by 750-fold, into the nanomolar range where it may be unable to compete for free Zn in the cell. With the exception of the S134N metal-binding variant, the Zn affinity of disulfide-oxidized SOD1 monomers showed little sensitivity to amino acid replacements. These results suggest a model for SOD1 aggregation where the constant synthesis of ALS-variants of SOD1 on ribosomes provides a pool of species in which the increased population of the unfolded state may favor aggregation over productive folding to the stable native dimeric state.

DOI of Published Version

10.1016/j.jmb.2010.02.034

Source

Kayatekin, C., Zitzewitz, J.A. and Matthews, C.R., Disulfide-Reduced ALS Variants of Cu, Zn Superoxide Dismutase Exhibit Increased Populations of Unfolded Species, Journal of Molecular Biology (2010). Link to article on publisher's website

Journal/Book/Conference Title

Journal of molecular biology

Related Resources

Link to article in PubMed

PubMed ID

20184893

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