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SOD1 associates to membranes in its folded apo-state
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Department of Biochemistry and Biophysics, Stockholm University, 10691 Stockholm, Sweden.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease accompanied by misfolding and intracellular deposition of superoxide dismutase 1 (SOD1). Although the molecular details behind this misfolding process are yet poorly understood, increasing evidence suggest that SOD1 is most susceptible to misfolding in its metal-free and relatively unstable apo-state. Here, we addressed the question, if misfolding and aggregation of SOD1 involves erroneous interactions with membranes as has been implicated for the Aβ peptide in Alzheimers disease. To examine this possibility we subjected various apo SOD1 variants to the presence of different membrane systems. The results reveal that wild type apoSOD1 but to less extent destabilized ALS mutations interact with charged vesicles under physiologically relevant conditions, thereby acquiring pronounced helical structural features. As the data further show, the protein binds to the membranes by an electrostatically driven mechanism, which requires a folded apo-state conformation and a negative membrane surface potential. Unfolded SOD1 molecules show no appreciable affinity to the membrane surfaces yielding a correlation between increased stability, i. e. occupancy of folded molecules and extend of membrane association. Since this trend opposes the correlation between decreased SOD1 stability and progression of neural damage, the results suggest that membrane association is not part of the ALS mechanism. An explanation could be that the observed membrane association of apo SOD1 is reversible and does not ‘bleed out’ in irreversible aggregation as observed for other precursors of protein-misfolding diseases.

National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
URN: urn:nbn:se:umu:diva-26314OAI: oai:DiVA.org:umu-26314DiVA: diva2:241776
Available from: 2009-10-05 Created: 2009-10-05 Last updated: 2011-08-19Bibliographically approved
In thesis
1. SOD1´s Law: An Investigation of ALS Provoking Properties in SOD1
Open this publication in new window or tab >>SOD1´s Law: An Investigation of ALS Provoking Properties in SOD1
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Proteins are the most important molecules in the cell since they take care of most of the biological functions which resemble life. To ensure that everything is working properly the cell has a rigorous control system to monitor the proper function of its proteins and sends old or dysfunctional proteins for degradation. Unfortunately, this system sometimes fails and the once so vital proteins start to misbehave or to accumulate and in the worst case scenario these undesired processes cause the death of their host. One example is Amyotrophic Lateral Sclerosis (ALS); a progressive and always fatal neurodegenerative disorder that is proposed to derive from accumulation of aberrant proteins. Over 140 mutations in the human gene encoding the cytosolic homodimeric enzyme Cu/Zn-Superoxide Dismutase (SOD1) are linked to ALS. The key event in SOD1 associated ALS seems to be the pathological formation of toxic protein aggregates as a result of initially unfolded or partly structured SOD1-mutants.

Here, we have compared the folding behaviour of a set of ALS associated SOD1 mutants. Based on our findings we propose that SOD1 mediated ALS can be triggered by a decrease in protein stability but also by mutations which reduce the net charge of the protein. Both findings are in good agreement with the hypothesis for protein aggregation.

SOD1 has also been found to be able to interact with mitochondrial membranes and SOD1 inclusions have been detected in the inter-membrane space of mitochondria originating from the spinal cord. The obvious question then arose; does the misfolding and aggregation of SOD1 involve erroneous interactions with membranes?

Here, we could show that there is an electrostatically driven interaction between the reduced apo SOD1 protein including ALS associated SOD1-mutants and charged lipid membrane surfaces. This association process changes the secondary structures of these mutants in a way quite different from the situation found in membrane free aqueous environment. However, the result show that mutants interact with charged lipid vesicles to lesser extent than wildtype SOD1. This opposes the correlation between decreased SOD1 stability and disease progression. We therefore suggest that the observed interaction is not a primary cause in the ALS mechanism.

Place, publisher, year, edition, pages
Umeå: Kemiska instsitutionen, Umeå universitet, 2009. 65 p.
Keyword
ALS, amyotrophic lateral sclerosis, SOD1, protein folding, membrane interaction, aggregates, survival time, repulsive charge
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:umu:diva-26319 (URN)978-91-7264-856-2 (ISBN)
Distributor:
Kemi, 90187, Umeå
Public defence
2009-10-30, KB3B1, Umeå universitet, KBC, Linnaeus väg 6, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2009-10-09 Created: 2009-10-05 Last updated: 2009-10-09Bibliographically approved

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