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Tim23, a protein import component of the mitochondrial inner membrane, is required for normal activity of the
T A Lohret1, R E Jensen, K W Kinnally
1Department of Biological Sciences, University at Albany, SUNY, New York 12222, USA.
Abstract:
We previously showed that the conductance of a mitochondrial inner membrane channel, called MCC, was specifically blocked by peptides corresponding to mitochondrial import signals. To determine if MCC plays a role in protein import, we examined the relationship between MCC and Tim23p, a component of the protein import complex of the mitochondrial inner membrane. We find that antibodies against Tim23p, previously shown to inhibit mitochondrial protein import, inhibit MCC activity. We also find that MCC activity is altered in mitochondria isolated from yeast carrying the tim23-1 mutation. In contrast to wild-type MCC, we find that the conductance of MCC from the tim23-1 mutant is not significantly blocked by mitochondrial presequence peptides. Tim23 antibodies and the tim23-1 mutation do not, however, alter the activity of PSC, a presequence-peptide sensitive channel in the mitochondrial outer membrane. Our results show that Tim23p is required for normal MCC activity and raise the possibility that precursors are translocated across the inner membrane through the pore of MCC.
Insights
Mitochondrial inner membrane channel (MCC) activity is regulated by Tim23p, a key protein import component. This suggests MCC may facilitate protein translocation across the inner mitochondrial membrane.
Area of Science:
- Mitochondrial biology
- Protein import mechanisms
- Membrane transport
Background:
- Mitochondrial inner membrane channel (MCC) conductance is blocked by mitochondrial import signal peptides.
- Tim23p is a crucial component of the protein import machinery in the mitochondrial inner membrane.
Purpose of the Study:
- To investigate the functional relationship between MCC and Tim23p in mitochondrial protein import.
- To determine if MCC plays a role in the translocation of proteins across the inner mitochondrial membrane.
Main Methods:
- Utilized antibodies against Tim23p to assess their effect on MCC activity.
- Examined MCC activity in mitochondria isolated from yeast strains with a tim23-1 mutation.
- Assessed the impact of Tim23p manipulation on PSC, a mitochondrial outer membrane channel.
Main Results:
- Antibodies against Tim23p inhibited MCC activity, mirroring their known effect on protein import.
- MCC activity was altered in tim23-1 mutant mitochondria, showing reduced sensitivity to presequence peptides.
- Tim23p manipulation did not affect the activity of the outer membrane channel PSC.
Conclusions:
- Tim23p is essential for the normal function of MCC.
- These findings support a model where MCC acts as the pore for precursor protein translocation across the inner mitochondrial membrane.