The mitochondrial import receptor Tom70 (translocase of the mitochondrial outer membrane 70) interacts with chaperone–preprotein complexes through two domains: one that binds Hsp70 (heat-shock protein 70)/Hsc70 (heat-shock cognate 70) and Hsp90, and a second that binds preproteins. The oligomeric state of Tom70 has been controversial, with evidence for both monomeric and homodimeric forms. In the present paper, we report that the functional state of human Tom70 appears to be a monomer with mechanistic implications for its function in mitochondrial protein import. Based on analytical ultracentrifugation, cross-linking, size-exclusion chromatography and multi-angle light scattering, we found that the soluble cytosolic fragment of human Tom70 exists in equilibrium between monomer and dimer. A point mutation introduced at the predicted dimer interface increased the percentage of monomeric Tom70. Although chaperone docking to the mutant was the same as to the wild-type, the mutant was significantly more active in preprotein targeting. Cross-linking also demonstrated that the mutant formed stronger contacts with preprotein. However, cross-linking of full-length wild-type Tom70 on the mitochondrial membrane showed little evidence of homodimers. These results indicate that the Tom70 monomers are the functional form of the receptor, whereas the homodimers appear to be a minor population, and may represent an inactive state.
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Research Article|
July 14 2010
Human mitochondrial import receptor Tom70 functions as a monomer
Anna C. Y. Fan;
Anna C. Y. Fan
*Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 0B1
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Lisandra M. Gava;
Lisandra M. Gava
†Institute of Chemistry, University of Campinas (UNICAMP), Campinas, SP, Brazil
‡Institute of Biology, University of Campinas (UNICAMP), Campinas, SP 13083-970, Brazil
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Carlos H. I. Ramos;
Carlos H. I. Ramos
†Institute of Chemistry, University of Campinas (UNICAMP), Campinas, SP, Brazil
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Jason C. Young
Jason C. Young
1
*Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 0B1
1To whom correspondence should be addressed (email jason.young2@mcgill.ca).
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Publisher: Portland Press Ltd
Received:
December 07 2009
Revision Received:
May 16 2010
Accepted:
May 26 2010
Accepted Manuscript online:
May 26 2010
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2010 Biochemical Society
2010
Biochem J (2010) 429 (3): 553–563.
Article history
Received:
December 07 2009
Revision Received:
May 16 2010
Accepted:
May 26 2010
Accepted Manuscript online:
May 26 2010
Citation
Anna C. Y. Fan, Lisandra M. Gava, Carlos H. I. Ramos, Jason C. Young; Human mitochondrial import receptor Tom70 functions as a monomer. Biochem J 1 August 2010; 429 (3): 553–563. doi: https://doi.org/10.1042/BJ20091855
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