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Changed membrane integration and catalytic site conformation are two mechanisms behind the increased Aβ42/Aβ40 ratio by presenilin 1 familial Alzheimer-linked mutations.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2014 (English)In: FEBS Open Bio, E-ISSN 2211-5463, Vol. 4, 393-406 p.Article in journal (Refereed) Published
Abstract [en]

The enzyme complex γ-secretase generates amyloid β-peptide (Aβ), a 37-43-residue peptide associated with Alzheimer disease (AD). Mutations in presenilin 1 (PS1), the catalytical subunit of γ-secretase, result in familial AD (FAD). A unifying theme among FAD mutations is an alteration in the ratio Aβ species produced (the Aβ42/Aβ40 ratio), but the molecular mechanisms responsible remain elusive. In this report we have studied the impact of several different PS1 FAD mutations on the integration of selected PS1 transmembrane domains and on PS1 active site conformation, and whether any effects translate to a particular amyloid precursor protein (APP) processing phenotype. Most mutations studied caused an increase in the Aβ42/Aβ40 ratio, but via different mechanisms. The mutations that caused a particular large increase in the Aβ42/Aβ40 ratio did also display an impaired APP intracellular domain (AICD) formation and a lower total Aβ production. Interestingly, seven mutations close to the catalytic site caused a severely impaired integration of proximal transmembrane/hydrophobic sequences into the membrane. This structural defect did not correlate to a particular APP processing phenotype. Six selected FAD mutations, all of which exhibited different APP processing profiles and impact on PS1 transmembrane domain integration, were found to display an altered active site conformation. Combined, our data suggest that FAD mutations affect the PS1 structure and active site differently, resulting in several complex APP processing phenotypes, where the most aggressive mutations in terms of increased Aβ42/Aβ40 ratio are associated with a decrease in total γ-secretase activity.

Place, publisher, year, edition, pages
2014. Vol. 4, 393-406 p.
Keyword [en]
Alzheimer disease, γ-Secretase, Membrane integration, Amyloid b-peptide, Protein structure
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-109355DOI: 10.1016/j.fob.2014.04.006ISI: 000346278200050PubMedID: 24918054OAI: oai:DiVA.org:su-109355DiVA: diva2:764414
Available from: 2014-11-19 Created: 2014-11-19 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Integration and topology of membrane proteins related to diseases
Open this publication in new window or tab >>Integration and topology of membrane proteins related to diseases
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Membranes are boundaries that separate the cell from the external environment.   Membrane proteins can function as e.g. receptors and channels, allowing cells to communicate with the exterior and molecules to pass through the membrane. The biogenesis of membrane proteins involves a protein-conducting channel that aids the hydrophobic segments to partition into the membrane and translocate the hydrophilic loops. Membrane proteins need to fold to its native conformation including post-translational modifications and assembly with other proteins and/or cofactors. If this regulated pathway goes wrong the degradation machinery degrades the protein. If the system is failing can result in serious disorders. The main focus in this thesis is membrane proteins associated to diseases.

We have studied mutations in the gene of presenilin 1, which is involved in Alzheimer’s disease. We found that some mutations affect the structure and other the function of the PS1. URG7 is an unknown protein associated with liver cancer. We suggest it is localized and targeted to the ER membrane, having an NoutCin topology. SP-C is important for our lungs to function. Mutations can cause the protein to aggregate. We have studied the highly Val-rich transmembrane segment (poly-Val) and its analogue (poly-Leu) and show that poly-Leu folds into a more compact conformation than poly-Val. We show that the C-terminal chaperon-like BRICHOS domain interacts with the ER membrane, suggesting an involvement in poly-Val folding. We have also confirmed the topology of URG7, MRP6 and SP-C poly-Val/Leu using gGFP that is fused to the C-terminal of the protein.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm Univeristy, 2015. 76 p.
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-113397 (URN)978-91-7649-094-5 (ISBN)
Public defence
2015-03-06, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense paper 3 was unpublished and had a status as manuscript.

Available from: 2015-02-12 Created: 2015-01-29 Last updated: 2016-02-23Bibliographically approved

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