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Lipid-protein interactions. The mitochondrial complex III-phosphatidylcholine-water system
J M Valpuesta1, F M Goñi, A Alonso
1Department of Biochemistry, Faculty of Science, University of the Basque Country, Bilbao, Spain.
Biochimica Et Biophysica Acta
|July 21, 1988
Summary
Reconstituting bovine heart mitochondrial complex III into lipid bilayers revealed that phospholipids activate enzyme function. Increasing lipid content promotes bilayer formation and enhances complex III activity, suggesting phospholipids are essential activators.
Area of Science:
- Biochemistry
- Structural Biology
- Membrane Proteins
Background:
- Mitochondrial complex III (ubiquinol-cytochrome-c reductase) is crucial for cellular respiration.
- Understanding its interaction with lipids is key to elucidating its function.
- Reconstitution into artificial membranes allows for controlled study of lipid-protein interactions.
Purpose of the Study:
- To investigate the impact of varying lipid/protein ratios on the structure and function of bovine heart mitochondrial complex III.
- To determine the role of phospholipids in the activity and conformation of complex III.
- To propose a kinetic model for phospholipid activation of complex III.
Main Methods:
- Reconstitution of complex III into phosphatidylcholine bilayers.
- Electron microscopy for structural analysis.
- Differential scanning calorimetry and Arrhenius plots for functional and thermal analysis.
- Visible and Fourier-transform infrared spectroscopy for conformational changes.
Main Results:
- Complex III incorporates into phosphatidylcholine bilayers in an active conformation.
- Low lipid/protein ratios lead to protein aggregation; higher ratios promote bilayer and vesicle formation.
- Enzyme activity increases with lipid content, approaching a saturation point.
- Spectroscopic data indicate changes in heme environment polarity and protein secondary structure with increasing lipid proportion.
Conclusions:
- Phospholipids act as essential activators for bovine heart mitochondrial complex III.
- Lipid/protein ratios significantly influence complex III structure, from aggregation to vesicle formation.
- A kinetic model suggests phospholipids bind to unspecific, independent sites, activating the enzyme.