| 1. |
- Khan, Ashhar, et al.
(författare)
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Adsorption of unfolded Cu/Zn superoxide dismutase onto hydrophobic surfaces catalyzes its formation of amyloid fibrils
- 2019
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Ingår i: Protein Engineering Design & Selection. - : Oxford University Press (OUP). - 1741-0126 .- 1741-0134. ; 32:2, s. 77-85
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular aggregates of superoxide dismutase 1 (SOD1) are associated with amyotrophic lateral sclerosis. In vivo, aggregation occurs in a complex and dense molecular environment with chemically heterogeneous surfaces. To investigate how SOD1 fibril formation is affected by surfaces, we used an in vitro model system enabling us to vary the molecular features of both SOD1 and the surfaces, as well as the surface area. We compared fibril formation in hydrophilic and hydrophobic sample wells, as a function of denaturant concentration and extraneous hydrophobic surface area. In the presence of hydrophobic surfaces, SOD1 unfolding promotes fibril nucleation. By contrast, in the presence of hydrophilic surfaces, increasing denaturant concentration retards the onset of fibril formation. We conclude that the mechanism of fibril formation depends on the surrounding surfaces and that the nucleating species might correspond to different conformational states of SOD1 depending on the nature of these surfaces.
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| 2. |
- Khan, Ashhar, et al.
(författare)
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Cu/Zn Superoxide Dismutase Forms Amyloid Fibrils under Near-Physiological Quiescent Conditions : The Roles of Disulfide Bonds and Effects of Denaturant
- 2017
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Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 8:9, s. 2019-2026
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Tidskriftsartikel (refereegranskat)abstract
- Cu/Zn superoxide dismutase (SOD1) forms intracellular aggregates that are pathological indicators of amyotrophic lateral sclerosis. A large body of research indicates that the entry point to aggregate formation is a monomeric, metal-ion free (apo), and disulfide-reduced species. Fibril formation by SOD1 in vitro has typically been reported only for harsh solvent conditions or mechanical agitation. Here we show that monomeric apo-SOD1 in the disulfide-reduced state forms fibrillar aggregates under near-physiological quiescent conditions. Monomeric apo-SOD1 with an intact intramolecular disulfide bond is highly resistant to aggregation under the same conditions. A cysteine-free variant of SOD1 exhibits fibrillization behavior and fibril morphology identical to those of disulfide-reduced SOD1, firmly establishing that intermolecular disulfide bonds or intramolecular disulfide shuffling are not required for aggregation and fibril formation. The decreased lag time for fibril formation resulting from reduction of the intramolecular disulfide bond thus primarily reflects the decreased stability of the folded state relative to partially unfolded states, rather than an active role of free sulfhydryl groups in mediating aggregation. Addition of urea to increase the amount of fully unfolded SOD1 increases the lag time for fibril formation, indicating that the population of this species does not dominate over other factors in determining the onset of aggregation. Our results contrast with previous results obtained for agitated samples, in which case amyloid formation was accelerated by denaturant. We reconcile these observations by suggesting that denaturants destabilize monomeric and aggregated species to different extents and thus affect nucleation and growth.
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