Title

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

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Date

2-22-2010

Document Type

Article

Medical Subject Headings

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

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.

Rights and Permissions

Citation: Kayatekin, C., Zitzewitz, J.A. & 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

Related Resources

Link to article in PubMed

PubMed ID

20184893