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Tom40 protein import channel binds to non-native proteins and prevents their aggregation

Nature Structural & Molecular Biology volume 10, pages 988–994 (2003)Cite this article

Abstract

Mitochondria contain the translocator of the outer mitochondrial membrane (TOM) for protein entry into the organelle, and its subunit Tom40 forms a protein-conducting channel. Here we report the role of Tom40 in protein translocation across the membrane. The site-specific photocrosslinking experiment revealed that translocating unfolded or loosely folded precursor segments of up to 90 residues can be associated with Tom40. Purified Tom40 bound to non-native proteins and suppressed their aggregation when they are prone to aggregate. A denatured protein bound to the Tom40 channel blocked the protein import into mitochondria. These results indicate that, in contrast to the nonstick tunnel of the ribosome for polypeptide exit, the Tom40 channel offers an optimized environment to translocating non-native precursor proteins by preventing their aggregation.

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Figure 1: Site-specific photocrosslinking of the MTX-arrested pb2(330)-DHFR.
Figure 2: Proteinase K digestion of the MTX-arrested pb2(330)-DHFR.
Figure 3: Tom40 crosslinked to unfolded or loosely folded segments of the MTX-arrested cytochrome b2–DHFR fusion proteins.
Figure 4: Tom40 binds to and/or suppresses aggregation of non-native proteins.
Figure 5: Blocking of protein import into mitochondria by urea-denatured proteins.

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Acknowledgements

We acknowledge support of this work by Grants-in-aid for Scientific Research from the Japan Ministry of Education, Culture, Sports Science and Technology (MEXT), a grant from Japan Science and Technology Agency (T.E.) and a Grant for Joint Research Project in Korea (I.S.). We thank T. Hohsaka and M. Sisido for the advice on charging of BPA to suppressor tRNA, and members of the Endo laboratory for discussions and comments. M.E. is a Japan Society for the Promotion of Science (JSPS) Research Fellow.

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Authors and Affiliations

  1. Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan

    Masatoshi Esaki, Takashi Kanamori, Shuh-ichi Nishikawa & Toshiya Endo

  2. Department of Chemistry, Yonsei University, Seoul, 120-749, Korea

    Injae Shin

  3. Genomics Institute of the Novartis Research Foundation, San Diego, 92121, California, USA

    Peter G Schultz

  4. Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Japan

    Toshiya Endo

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  1. Masatoshi Esaki
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Correspondence to Toshiya Endo.

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Esaki, M., Kanamori, T., Nishikawa, Si. et al. Tom40 protein import channel binds to non-native proteins and prevents their aggregation. Nat Struct Mol Biol 10, 988–994 (2003). https://doi.org/10.1038/nsb1008

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