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.
Bibliographical noteFunding Information:
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.
All Science Journal Classification (ASJC) codes
- Structural Biology