Interactions of the human mitochondrial protein import receptor, hTom20, with precursor proteins in vitro reveal pleiotropic specificities and different receptor domain requirements.
Tom20 is part of a multiple component, dynamic complex that functions to import specific cytosolic proteins into or through the outer membrane of the mitochondrion. To analyze the contribution of Tom20 to precursor protein recognition, the cytosolic domain of the human mitochondrial import receptor, hTom20, has been expressed as a fusion protein with glutathione S-transferase and conditions established to measure specific interactions of the receptor component with precursor proteins in vitro. Reconstitution of receptor binding from purified components revealed that a prototypic matrix-destined precursor protein, pODHFR, interacts with Tom20 by a mechanism that is dependent on an active matrix targeting signal but does not require cytosolic components or ATP. Binding was influenced by both salt concentration and detergent. The effect of salt or detergent, however, varied for different precursor proteins. In particular, detergent selectively enhanced binding of pODHFR to receptor, possibly because of induced changes in the structure of the signal sequence. Finally, mutations were introduced into hTom20 which had a dramatic effect on binding of some precursor proteins but not on others. Taken together, the results suggest that hTom20 recognizes and physically interacts with precursor proteins bearing a diverse array of topogenic sequences and that such pleiotropic specificity for these precursor proteins may involve different domains within the receptor molecule.
Schleiff
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Department of Biochemistry, McGill University, Montreal H3G 1Y6, Canada.
Shore
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Goping
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000906:Antibodies / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D005033:Ethylmaleimide / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D008958:Models, Molecular; D009154:Mutation; D009954:Ornithine Carbamoyltransferase / Q000235:genetics / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000071256:Uncoupling Protein 1
D000906:Antibodies; D002352:Carrier Proteins; D003902:Detergents; D004792:Enzyme Precursors; D007473:Ion Channels; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C084008:TOMM20 protein, human; D000071256:Uncoupling Protein 1; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; D000226:Mitochondrial ADP, ATP Translocases; D013762:Tetrahydrofolate Dehydrogenase; C052289:preornithine carbamoyltransferase; D009954:Ornithine Carbamoyltransferase; D005033:Ethylmaleimide