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Tom5 functionally links mitochondrial preprotein receptors to the general import pore
K Dietmeier1, A Hönlinger, U Bömer
1Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
Abstract:
Most mitochondrial proteins are synthesized as preproteins on cytosolic polysomes and are subsequently imported into the organelle. The mitochondrial outer membrane contains a multisubunit preprotein translocase (Tom) which has receptors on the cytosolic side and a general import pore (GIP) in the membrane. Tom20-Tom22 and Tom70-Tom37 function as import receptors with a preference for preproteins that have amino-terminal presequences or internal targeting information, respectively. Tom40 is an essential constituent of the GIP, whereas Tom6 and Tom7 modulate the assembly and dissociation of the Tom machinery. Here we report the identification of Tom5, a small subunit that has a crucial role importing preproteins destined for all four mitochondrial subcompartments. Tom5 has a single membrane anchor and a cytosolic segment with a negative net charge, and accepts preproteins from the receptors and mediates their insertion into the GIP. We conclude that Tom5 represents a functional link between surface receptors and GIP, and is part of an 'acid chain' that guides the stepwise transport of positively charged mitochondrial targeting sequences.
Insights
Researchers identified Tom5, a crucial protein import component. Tom5 links surface receptors to the general import pore, facilitating mitochondrial protein transport.
Area of Science:
- Mitochondrial biology
- Protein import mechanisms
- Cellular and molecular biology
Background:
- Mitochondrial proteins are synthesized in the cytosol and imported into the organelle.
- The mitochondrial outer membrane translocase (Tom) complex mediates protein import.
- Key components include receptors (Tom20-Tom22, Tom70-Tom37) and the general import pore (Tom40).
Purpose of the Study:
- To identify novel subunits of the mitochondrial protein import machinery.
- To elucidate the function of newly discovered Tom complex components in protein translocation.
Main Methods:
- Protein identification and characterization.
- Analysis of protein interactions within the Tom complex.
- Functional assays for mitochondrial protein import.
Main Results:
- Identification of Tom5, a small subunit of the Tom complex.
- Tom5 possesses a single membrane anchor and a negatively charged cytosolic segment.
- Tom5 accepts preproteins from receptors and inserts them into the general import pore.
Conclusions:
- Tom5 is essential for importing proteins into all mitochondrial subcompartments.
- Tom5 acts as a functional bridge between Tom receptors and the general import pore.
- Tom5 is part of an 'acid chain' mechanism guiding positively charged mitochondrial targeting sequences.