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Modulation of apolipoprotein E structure by domain interaction: differences in lipid-bound and lipid-free forms
Danny M Hatters1, Madhu S Budamagunta, John C Voss
1Gladstone Institutes of Cardiovascular and Neurological Diseases, San Francisco, California 94158, USA.
The Journal of Biological Chemistry
|August 4, 2005
Summary
Apolipoprotein E4 (apoE4) exhibits stronger domain interaction than apoE3, increasing Alzheimer and cardiovascular disease risk. This structural difference is confirmed by biophysical methods, revealing distinct apoE conformations based on lipid binding.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Apolipoprotein E (apoE) isoforms, particularly apoE4, are linked to Alzheimer and cardiovascular diseases.
- The domain interaction hypothesis suggests altered apoE4 structure contributes to disease risk.
- Direct physical evidence for this domain interaction has been lacking.
Purpose of the Study:
- To provide direct physical evidence for the domain interaction concept in apolipoprotein E.
- To compare the domain interaction between apoE4 and apoE3 isoforms.
- To investigate how lipid binding affects apoE conformation.
Main Methods:
- Fluorescence resonance energy transfer (FRET) to measure spatial proximity of apoE domains.
- Electron paramagnetic resonance (EPR) spectroscopy to probe domain distances.
- Utilized both lipid-free and phospholipid-bound apoE models.
Main Results:
- Both FRET and EPR confirmed closer domain proximity in apoE4 compared to apoE3, indicating stronger domain interaction.
- EPR data showed that apoE4 domains move apart upon binding to triglyceride-rich emulsion particles, resembling apoE3 distances.
- These findings demonstrate that apoE adopts different conformations depending on the lipid environment.
Conclusions:
- Domain interaction is an intrinsic structural property of the apoE4 isoform.
- The distinct conformations of apoE isoforms are influenced by the type of lipids they bind.
- Understanding these structural differences is crucial for elucidating apoE4's role in neurodegenerative and cardiovascular diseases.