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Proteinaceous receptors for the import of mitochondrial precursor proteins
Abstract:
Mild trypsin treatment of isolated Neurospora mitochondria strongly inhibits their ability to bind and import the precursors of several mitochondrial proteins. Evidence is presented for two proteins, the ADP/ATP carrier and the mitochondrial porin, that specific binding of the precursors to the outer surface of the mitochondria is affected by the protease treatment. We suggest that the receptors that mediate the import of these two precursors are proteinaceous. Treatment of mitochondria with elastase also inhibits the binding and import of the ADP/ATP carrier and the porin. In contrast the import of the precursors of subunits 2 and 9 of the mitochondrial proton-translocating ATPase was unaffected by elastase treatment at the concentrations used. We suggest that the import pathways of the latter two proteins are distinct from those of the ADP/ATP carrier and the porin.
Insights
Protease treatment inhibits mitochondrial protein import by affecting precursor binding, suggesting proteinaceous receptors. Different proteins utilize distinct import pathways in Neurospora mitochondria.
Area of Science:
- Mitochondrial biology
- Protein import mechanisms
- Fungal cell biology
Background:
- Mitochondria import numerous proteins synthesized in the cytoplasm.
- Specific receptors on the mitochondrial surface mediate protein import.
- The precise nature of these receptors and distinct import pathways remain under investigation.
Purpose of the Study:
- To investigate the role of surface receptors in mitochondrial protein import.
- To determine if different mitochondrial proteins utilize distinct import pathways.
- To characterize the proteinaceous nature of import receptors.
Main Methods:
- Isolated Neurospora mitochondria were treated with mild trypsin and elastase.
- The binding and import of precursor proteins were analyzed.
- Specific protein precursors studied included ADP/ATP carrier, mitochondrial porin, and subunits of the proton-translocating ATPase.
Main Results:
- Trypsin treatment inhibited the binding and import of ADP/ATP carrier and porin precursors.
- Elastase treatment similarly affected ADP/ATP carrier and porin import.
- Import of ATPase subunit precursors was unaffected by elastase, suggesting distinct pathways.
Conclusions:
- Mitochondrial protein import receptors are likely proteinaceous.
- The ADP/ATP carrier and porin share an import pathway sensitive to protease treatment.
- Mitochondrial proton-translocating ATPase subunits utilize a distinct import pathway.