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Fibrillation precursor of superoxide dismutase 1 revealed by gradual tuning of the protein-folding equilibrium
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
2012 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 44, 17868-17873 p.Article in journal (Refereed) Published
Abstract [en]

Although superoxide dismutase 1 (SOD1) stands out as a relatively soluble protein in vitro, it can be made to fibrillate by mechanical agitation. The mechanism of this fibrillation process is yet poorly understood, but attains considerable interest due to SOD1's involvement in the neurodegenerative disease amyotrophic lateral sclerosis (ALS). In this study, we map out the apoSOD1 fibrillation process from how it competes with the global folding events at increasing concentrations of urea: We determine how the fibrillation lag time (τ(lag)) and maximum growth rate (ν(max)) depend on gradual titration of the folding equilibrium, from the native to the unfolded state. The results show that the agitation-induced fibrillation of apoSOD1 uses globally unfolded precursors and relies on fragmentation-assisted growth. Mutational screening and fibrillation m-values (∂ log τ(lag)/∂[urea] and ∂ log ν(max)/∂[urea]) indicate moreover that the fibrillation pathway proceeds via a diffusely bound transient complex that responds to the global physiochemical properties of the SOD1 sequence. Fibrillation of apoSOD1, as it bifurcates from the denatured ensemble, seems thus mechanistically analogous to that of disordered peptides, save the competing folding transition to the native state. Finally, we examine by comparison with in vivo data to what extent this mode of fibrillation, originating from selective amplification of mechanically brittle aggregates by sample agitation, captures the mechanism of pathological SOD1 aggregation in ALS.

Place, publisher, year, edition, pages
2012. Vol. 109, no 44, 17868-17873 p.
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-80510DOI: 10.1073/pnas.1201795109ISI: 000311149900044OAI: oai:DiVA.org:su-80510DiVA: diva2:556034
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Protein folding without loops and charges
Open this publication in new window or tab >>Protein folding without loops and charges
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Going down the folding funnel, proteins may sample a wide variety of conformations, some being outright detrimental to the organism. Yet, the vast majority of polypeptide molecules avoid such pitfalls. Not only do they reach the native minimum of the energy landscape; they do so via blazingly fast, biased, routes. This specificity and speed is remarkable, as the surrounding solution is filled to the brim with other molecules that could potentially interact with the protein and in doing so stabilise non-native, potentially toxic, conformations. How such incidents are avoided while maintaining native structure and function is not understood. 

This doctoral thesis argues that protein structure and function can be separated in the folding code of natural protein sequences by use of multiple partly uncoupled factors that act in a concerted fashion. More specifically, we demonstrate that: i) Evolutionarily conserved functional and regulatory elements can be excised from a present day protein, leaving behind an independently folded protein scaffold. This suggests that the dichotomy between functional and structural elements can be preserved during the course of protein evolution. ii) The ubiquitous charges on soluble protein surfaces are not required for protein folding in biologically relevant timescales, but are critical to intermolecular interaction. Monomer folding can be driven by hydrophobicity and hydrogen bonding alone, while functional and structural intermolecular interaction depends on the relative positions of charges that are not required for the native bias inherent to the folding mechanism. It is possible that such uncoupling reduces the probability of evolutionary clashes between fold and function. Without such a balancing mechanism, functional evolution might pull the carpet from under the feet of structural integrity, and vice versa. These findings have implications for both de novo protein design and the molecular mechanisms behind diseases caused by protein misfolding.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2012. 70 p.
Keyword
protein folding, folding cooperativity, protein aggregation, protein charges, protein engineering
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-80512 (URN)978-91-7447-545-6 (ISBN)
Public defence
2012-10-26, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2012-10-04 Created: 2012-09-24 Last updated: 2012-10-01Bibliographically approved

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Lang, LisaKurnik, MartinDanielsson, JensOliveberg, Mikael
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