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SOD1´s Law: An Investigation of ALS Provoking Properties in SOD1
Umeå University, Faculty of Science and Technology, Chemistry.
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 [en]
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: urn:nbn:se:umu:diva-26319ISBN: 978-91-7264-856-2 (print)OAI: oai:DiVA.org:umu-26319DiVA: diva2:241976
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
List of papers
1. Systematically perturbed folding patterns of amyotrophic lateral sclerosis (ALS)-associated SOD1 mutants
Open this publication in new window or tab >>Systematically perturbed folding patterns of amyotrophic lateral sclerosis (ALS)-associated SOD1 mutants
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2005 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, Vol. 102, no 28, 9754-9 p.Article in journal (Refereed) Published
Abstract [en]

Amyotrophic lateral sclerosis is a neurodegenerative syndrome associated with 114 mutations in the gene encoding the cytosolic homodimeric enzyme Cu/Zn superoxide dismutase (SOD). In this article, we report that amyotrophic lateral sclerosis-associated SOD mutations with distinctly different disease progression can be rationalized in terms of their folding patterns. The mutations are found to perturb the protein in multiple ways; they destabilize the precursor monomers (class 1), weaken the dimer interface (class 2), or both at the same time (class 1 + 2). A shared feature of the mutational perturbations is a shift of the folding equilibrium toward poorly structured SOD monomers. We observed a link, coupled to the altered folding patterns, between protein stability, net charge, and survival time for the patients carrying the mutations.

Place, publisher, year, edition, pages
National Academy of Sciences, 2005
Keyword
neurodegenerative disease, protein stability
Identifiers
urn:nbn:se:umu:diva-14675 (URN)10.1073/pnas.0501957102 (DOI)
Available from: 2007-11-22 Created: 2007-11-22 Last updated: 2009-10-07Bibliographically approved
2. Disordered proteins: Biological membranes as two-dimensional aggregation matrices
Open this publication in new window or tab >>Disordered proteins: Biological membranes as two-dimensional aggregation matrices
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2008 (English)In: Cell Biochemistry and Biophysics, ISSN 1085-9195, E-ISSN 1559-0283, Vol. 52, no 3, 175-189 p.Article, review/survey (Refereed) Published
Abstract [en]

Aberrant folded proteins and peptides are hallmarks of amyloidogenic diseases. However, the molecular processes that cause these proteins to adopt non-native structures in vivo and become cytotoxic are still largely unknown, despite intense efforts to establish a general molecular description of their behavior. Clearly, the fate of these proteins is ultimately linked to their immediate biochemical environment in vivo. In this review, we focus on the role of biological membranes, reactive interfaces that not only affect the conformational stability of amyloidogenic proteins, but also their aggregation rates and, probably, their toxicity. We first provide an overview of recent work, starting with findings regarding the amphiphatic amyloid-β protein (Aβ), which give evidence that membranes can directly promote aggregation, and that the effectiveness in this process can be related to the presence of specific neuronal ganglioside lipids. In addition, we discuss the implications of recent research (medin as an detailed example) regarding putative roles of membranes in the misfolding behavior of soluble, non-amphiphatic proteins, which are attracting increasing interest. The potential role of membranes in exerting the toxic action of misfolded proteins will also be highlighted in a molecular context. In this review, we discuss novel NMR-based approaches for exploring membrane–protein interactions, and findings obtained using them, which we use to develop a molecular concept to describe membrane-mediated protein misfolding as a quasi-two-dimensional process rather than a three-dimensional event in a biochemical environment. The aim of the review is to provide researchers with a general understanding of the involvement of membranes in folding/misfolding processes in vivo, which might be quite universal and important for future research concerning amyloidogenic and misfolding proteins, and possible ways to prevent their toxic actions.

Keyword
Membranes, Surface, Amyloid, Aggregation, NMR
Identifiers
urn:nbn:se:umu:diva-10887 (URN)10.1007/s12013-008-9033-4 (DOI)
Available from: 2008-12-02 Created: 2008-12-02 Last updated: 2017-12-14Bibliographically approved
3. Identification of property outliers among ALS-associated SOD1 mutations: Common effect on surface hydrogen bonds
Open this publication in new window or tab >>Identification of property outliers among ALS-associated SOD1 mutations: Common effect on surface hydrogen bonds
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

In good accord with the protein-aggregation hypothesis for neurodegenerative diseaseALS-associated SOD1 mutations are found to reduce structural stability or netrepulsive charge. Moreover there are weak indications that the ALS diseaseprogression is correlated with the degree of mutational impact on the SOD1 structure.A bottleneck for obtaining more conclusive information about these structure-diseaserelationships, however, is the large intrinsic variability in patient survival times andinsufficient disease statistics for the majority of ALS-provoking mutations. As analternative test of the structure-disease relationship we focus here on the SOD1 amutation that appears to be outliers in the data set. The results identify several ALSprovokingmutations whose only effect on apo SOD1 is the elimination orintroduction of a single charge, i.e., D76V/Y, D101N and N139D/K. Thethermodynamic stability and folding behaviour of these mutants are indistinguishablefrom the wildtype control, showing that structurally benign replacements of individualsurface charges are sufficient to trigger ALS. Moreover, D101N is a clear outlier inthe plot of stability loss vs. patient survival time by having too rapid diseaseprogression. Common to the identified mutations is that they truncate conserved saltlinksand/or H-bond networks in the functional loops IV or VII. The results show thatthe local impact of ALS-associated mutations on the SOD1 molecule can sometimesoverrun their global effects on stability and net repulsive charge, and point at theanalysis of property outliers as an efficient strategy for mapping out new ALSprovokingfeatures.

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-26315 (URN)
Available from: 2009-10-05 Created: 2009-10-05 Last updated: 2010-01-14
4. SOD1 associates to membranes in its folded apo-state
Open this publication in new window or tab >>SOD1 associates to membranes in its folded apo-state
(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:nbn:se:umu:diva-26314 (URN)
Available from: 2009-10-05 Created: 2009-10-05 Last updated: 2011-08-19Bibliographically approved
5. Electrostatic interactions between negatively charged phospolipid membranes and SOD1 protein: Effect of charge changing fALS mutations
Open this publication in new window or tab >>Electrostatic interactions between negatively charged phospolipid membranes and SOD1 protein: Effect of charge changing fALS mutations
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The neurodegenerative disease amyotrophic lateral sclerosis (ALS) is closely connected to single site mutations of the Cu/Zn superoxide dismutase (SOD1) protein, whose pathological conversion into misfolded aggregates is a hallmark of ALS. To explore the impact of protein net charge changing ALS relevant SOD1 mutations on their ability to interact with neuronal membranes and the consequences for their folding behaviour, we studied by circular dichroism the conformational changes of the SOD1pWT, SOD1N86D and SOD1N86K species in their apo-state in the presence of increasing amounts of negatively charged lipid bilayers.. The results clearly indicate an electrostatically driven association process, where the association event induces a pronounced increase in the helical character of the pWT and the N86D species, characterized by long patient survival times. To the opposite, the charge reducing N86K mutation shows more pronounced β-like features in the presence of membranes in comparison to the other two species; an observation which most likely reflects its reduced stability in its apo-state in combination with a very fast ALS progression.

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-26317 (URN)
Available from: 2009-10-05 Created: 2009-10-05 Last updated: 2010-01-14

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