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Multiple conformations of physiological membrane-bound cytochrome c
J D Cortese1, A L Voglino, C R Hackenbrock
1Department of Cell Biology and Anatomy and Laboratories for Cell Biology, The School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7090, USA.
Biochemistry
|June 13, 1998
Summary
Cytochrome c (cyt c) binding to mitochondrial membranes changes its structure and electron transport (ET) activity. This study reveals dynamic conformational changes and rapid exchange between soluble and membrane-bound cyt c forms.
Area of Science:
- Biochemistry
- Mitochondrial Biology
- Protein Conformation
Background:
- Cytochrome c (cyt c) is crucial for mitochondrial electron transport (ET).
- A fraction of cyt c remains membrane-bound at physiological ionic strength, with reduced ET activity.
- Understanding cyt c's membrane interactions is key to mitochondrial function.
Purpose of the Study:
- To investigate the in vitro formation and properties of membrane-bound cyt c (MB-cyt c).
- To characterize the conformational changes and ET activity of MB-cyt c under varying ionic conditions.
- To elucidate the dynamic exchange between soluble and membrane-bound cyt c conformations.
Main Methods:
- In vitro binding of cyt c to membranes (large and small unilamellar vesicles).
- Measurement of electron transport (ET) activity.
- Circular dichroism spectroscopy to analyze protein secondary structure.
- Ionic strength and temperature-dependent binding studies.
Main Results:
- Low ionic strength promotes a membrane-bound cyt c (MBL-cyt c) conformation with high ET activity, similar to soluble cyt c.
- MB-cyt c exhibits decreased alpha-helical content and increased beta-sheet structure.
- MB-cyt c converts to a more active form on the membrane and releases at physiological ionic strength.
- Binding and release are dynamic processes influenced by temperature.
Conclusions:
- Cyt c exists in soluble and membrane-bound conformations with similar ET activity.
- These conformations likely undergo rapid interconversion in mitochondria.
- Soluble proteins can transiently bind to biomembranes, influencing their function.