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Signal sequence region of mitochondrial precursor proteins binds to mitochondrial import receptor
1Laboratory of Cell Biology, Rockefeller University, Howard Hughes Medical Institute, New York, NY 10021.
Abstract:
An integral mitochondrial membrane protein (p32) of yeast has previously been molecularly cloned and sequenced and suggested to function as a mitochondrial import receptor. However, this protein has also been proposed to function as phosphate translocator [Guérin, B., Bukusoglu, C., Rakotomanana, F. & Wohlrab, H. (1990) J. Biol. Chem. 265, 19736-19741; Phelps, A., Schobert, C.T. & Wohlrab, H. (1991) Biochemistry 30, 248-252]. Here we have purified p32 after expression of its gene in Escherichia coli and assayed its ability to bind to various preproteins containing signal sequences for protein translocation into mitochondria, chloroplasts, or the endoplasmic reticulum. Our data suggest that p32 contains a binding site specific for the signal sequence region of mitochondrial preproteins. These data are consistent with the previous assignment of p32 as an import receptor and are discussed with regard to the apparently conflicting assignment of this protein as phosphate translocator.
Insights
Yeast mitochondrial protein p32 binds specifically to mitochondrial preprotein signal sequences. This finding supports its role as an import receptor, clarifying its function.
Area of Science:
- Mitochondrial biology
- Protein import mechanisms
- Molecular genetics
Background:
- Yeast mitochondrial membrane protein p32 has been cloned and sequenced.
- Previous studies suggest p32 functions as either a mitochondrial import receptor or a phosphate translocator.
Purpose of the Study:
- To investigate the function of yeast p32.
- To determine if p32 binds to preproteins destined for mitochondria, chloroplasts, or endoplasmic reticulum.
Main Methods:
- Purification of p32 expressed in Escherichia coli.
- Assay of p32 binding to various preproteins with different signal sequences.
Main Results:
- Purified p32 demonstrated specific binding to the signal sequence region of mitochondrial preproteins.
- Binding was not observed for preproteins targeted to chloroplasts or the endoplasmic reticulum.
Conclusions:
- The data strongly support the role of p32 as a mitochondrial import receptor.
- The findings help reconcile conflicting previous assignments of p32's function.