Exposure of hydrophobic surfaces initiates aggregation of diverse ALS-causing superoxide dismutase-1 mutants.
Bottom Line: The remarkable diversity of the effects of these mutations on SOD1 properties has suggested that they promote aggregation by a variety of mechanisms.Our results uncover the biochemical nature of the misfolded aggregation-prone intermediate and reconcile the seemingly diverse effects of ALS-causing mutations into a unifying mechanism.Furthermore, the method we describe here will be useful for investigating and interfering with aggregation of various proteins and thereby provide insight into the molecular mechanisms underlying many neurodegenerative diseases.
Affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.Show MeSH
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Mentions: Having found an unprecedented common feature for these diverse SOD1 mutants we then asked whether increased exposure of hydrophobic surfaces caused aggregation. We used conditions previously established to elicit mutant SOD1 aggregation to address this question, such as acidic pH in the presence or absence of a chelator. In buffer alone, or in the presence of as-purified SOD1WT or SOD1A4V, Sypro Orange fluorescence was very low, indicating that hydrophobic residues are buried in both SOD1WT and SOD1A4V, as expected for native proteins (Fig. 3a). At physiological temperature, Sypro Orange fluorescence increased dramatically only in the presence of EDTA-treated SOD1A4V, indicating that EDTA-treated SOD1A4V exhibited greater surface hydrophobicity than the SOD1WT exposed to the same condition, or the untreated proteins (Fig. 3a), as previously observed.13
Affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.