Transient structural distortion of metal-free Cu/Zn superoxide dismutase triggers aberrant oligomerization

Proc Natl Acad Sci U S A. 2009 Oct 27;106(43):18273-8. doi: 10.1073/pnas.0907387106. Epub 2009 Oct 14.

Abstract

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease linked to the misfolding of Cu/Zn superoxide dismutase (SOD1). ALS-related defects in SOD1 result in a gain of toxic function that coincides with aberrant oligomerization. The structural events triggering oligomerization have remained enigmatic, however, as is the case in other protein-misfolding diseases. Here, we target the critical conformational change that defines the earliest step toward aggregation. Using nuclear spin relaxation dispersion experiments, we identified a short-lived (0.4 ms) and weakly populated (0.7%) conformation of metal-depleted SOD1 that triggers aberrant oligomerization. This excited state emanates from the folded ground state and is suppressed by metal binding, but is present in both the disulfide-oxidized and disulfide-reduced forms of the protein. Our results pinpoint a perturbed region of the excited-state structure that forms intermolecular contacts in the earliest nonnative dimer/oligomer. The conformational transition that triggers oligomerization is a common feature of WT SOD1 and ALS-associated mutants that have widely different physicochemical properties. But compared with WT SOD1, the mutants have enhanced structural distortions in their excited states, and in some cases slightly higher excited-state populations and lower kinetic barriers, implying increased susceptibility to oligomerization. Our results provide a unified picture that highlights both (i) a common denominator among different SOD1 variants that may explain why diverse mutations cause the same disease, and (ii) a structural basis that may aid in understanding how different mutations affect disease propensity and progression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoenzymes / chemistry
  • Apoenzymes / genetics
  • Apoenzymes / metabolism
  • Disulfides / chemistry
  • Disulfides / metabolism
  • Humans
  • Models, Molecular
  • Mutation
  • Nuclear Magnetic Resonance, Biomolecular
  • Protein Multimerization*
  • Protein Structure, Quaternary*
  • Protein Structure, Tertiary
  • Superoxide Dismutase / chemistry*
  • Superoxide Dismutase / genetics
  • Superoxide Dismutase / metabolism
  • Superoxide Dismutase-1

Substances

  • Apoenzymes
  • Disulfides
  • SOD1 protein, human
  • Superoxide Dismutase
  • Superoxide Dismutase-1