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Cytochrome c binds to lipid domains in arrays of mitochondrial outer membrane channels
Abstract:
Computer-averaged electron microscopic images of negatively stained crystalline arrays of fungal mitochondrial outer-membrane channels in the presence and absence of cytochrome c were compared. Neither the apo- nor the holo- forms of cytochrome c significantly changed the stain distribution in the protein regions of the channel arrays. However, both forms of cytochrome c caused significant stain exclusion from the lipid domains in the arrays, suggesting binding of the polypeptides at these loci. The implications of binding of apocytochrome c to clusters of exposed phospholipids on the mitochondrial outer membrane are discussed with respect to the mechanism of uptake of this polypeptide by mitochondria.
Insights
Cytochrome c binds to lipid regions of fungal mitochondrial outer membranes, not protein channels. This binding may influence how mitochondria take up apocytochrome c.
Area of Science:
- Biochemistry
- Cell Biology
- Structural Biology
Background:
- Mitochondrial outer membranes contain protein channels crucial for transport.
- Cytochrome c is a key protein involved in mitochondrial function and apoptosis.
- The interaction of cytochrome c with the mitochondrial outer membrane is not fully understood.
Purpose of the Study:
- To investigate the binding sites of cytochrome c on fungal mitochondrial outer-membrane channels.
- To determine if cytochrome c interacts with protein or lipid components of the outer membrane.
Main Methods:
- Computer-averaged electron microscopy was used to analyze negatively stained crystalline arrays.
- Crystalline arrays of mitochondrial outer-membrane channels were examined with and without cytochrome c (apo- and holo- forms).
- Stain distribution was analyzed to infer binding interactions.
Main Results:
- Neither apo- nor holo-cytochrome c significantly altered stain distribution in the protein regions of the channel arrays.
- Both forms of cytochrome c caused significant stain exclusion from the lipid domains of the arrays.
- This suggests that cytochrome c binds to the lipid regions of the mitochondrial outer membrane.
Conclusions:
- Cytochrome c binds to lipid domains on the fungal mitochondrial outer membrane.
- This binding occurs independently of the protein channel structures.
- The interaction with exposed phospholipids may play a role in the uptake of apocytochrome c by mitochondria.