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Tim23, a protein import component of the mitochondrial inner membrane, is required for normal activity of the multiple conductance channel, MCC.

Lohret TA, Jensen RE, Kinnally KW - J. Cell Biol. (1997)

Bottom Line: We also find that MCC activity is altered in mitochondria isolated from yeast carrying the tim23-1 mutation.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.

View Article: PubMed Central - PubMed

Affiliation: Department 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.

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Rapid flickering induced by presequence peptides in  the micropipette solution is reduced in MCC from the tim23-1  mutant. Patches were excised from proteoliposomes containing  wild-type (A) or tim23-1 (B) mitochondrial inner membranes.  Typical current traces of MCC activity at −20 mV recorded from  different patches in the presence and absence of 100 μM yCOXIV1-13 peptide in the micropipette are shown. PO corresponds to  probability of occupying the open state.
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Figure 6: Rapid flickering induced by presequence peptides in the micropipette solution is reduced in MCC from the tim23-1 mutant. Patches were excised from proteoliposomes containing wild-type (A) or tim23-1 (B) mitochondrial inner membranes. Typical current traces of MCC activity at −20 mV recorded from different patches in the presence and absence of 100 μM yCOXIV1-13 peptide in the micropipette are shown. PO corresponds to probability of occupying the open state.

Mentions: We found that the electrical properties of MCC isolated from wild-type and tim23-1 strains were virtually identical (compare control current traces of Fig. 5 A with 5 B and Fig. 6 A with 6 B). In particular, MCC from both strains had the same peak conductance, predominant transition size, mean open time, and cation selectivity. Furthermore, permeability ratios for K+/Cl− were ∼6 for MCC from wildtype and tim23-1 patches with a 150:30 mM KCl gradient. Conductance through MCC from both strains was voltage dependent, i.e., MCC is predominantly open at low (e.g., 20 mV) but not high potentials of either polarity. The V0 (voltage where the probability of opening and closing are the same) at positive potentials was less than V0 at negative potentials for MCC from both wild-type and tim23-1 strains.


Tim23, a protein import component of the mitochondrial inner membrane, is required for normal activity of the multiple conductance channel, MCC.

Lohret TA, Jensen RE, Kinnally KW - J. Cell Biol. (1997)

Rapid flickering induced by presequence peptides in  the micropipette solution is reduced in MCC from the tim23-1  mutant. Patches were excised from proteoliposomes containing  wild-type (A) or tim23-1 (B) mitochondrial inner membranes.  Typical current traces of MCC activity at −20 mV recorded from  different patches in the presence and absence of 100 μM yCOXIV1-13 peptide in the micropipette are shown. PO corresponds to  probability of occupying the open state.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139772&req=5

Figure 6: Rapid flickering induced by presequence peptides in the micropipette solution is reduced in MCC from the tim23-1 mutant. Patches were excised from proteoliposomes containing wild-type (A) or tim23-1 (B) mitochondrial inner membranes. Typical current traces of MCC activity at −20 mV recorded from different patches in the presence and absence of 100 μM yCOXIV1-13 peptide in the micropipette are shown. PO corresponds to probability of occupying the open state.
Mentions: We found that the electrical properties of MCC isolated from wild-type and tim23-1 strains were virtually identical (compare control current traces of Fig. 5 A with 5 B and Fig. 6 A with 6 B). In particular, MCC from both strains had the same peak conductance, predominant transition size, mean open time, and cation selectivity. Furthermore, permeability ratios for K+/Cl− were ∼6 for MCC from wildtype and tim23-1 patches with a 150:30 mM KCl gradient. Conductance through MCC from both strains was voltage dependent, i.e., MCC is predominantly open at low (e.g., 20 mV) but not high potentials of either polarity. The V0 (voltage where the probability of opening and closing are the same) at positive potentials was less than V0 at negative potentials for MCC from both wild-type and tim23-1 strains.

Bottom Line: We also find that MCC activity is altered in mitochondria isolated from yeast carrying the tim23-1 mutation.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.

View Article: PubMed Central - PubMed

Affiliation: Department 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.

Show MeSH
Related in: MedlinePlus