Letter | Published:

A ribosome-associating factor chaperones tail-anchored membrane proteins

Nature volume 466, pages 11201124 (26 August 2010) | Download Citation

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Abstract

Hundreds of proteins are inserted post-translationally into the endoplasmic reticulum (ER) membrane by a single carboxy-terminal transmembrane domain (TMD)1. During targeting through the cytosol, the hydrophobic TMD of these tail-anchored (TA) proteins requires constant chaperoning to prevent aggregation or inappropriate interactions. A central component of this targeting system is TRC40, a conserved cytosolic factor that recognizes the TMD of TA proteins and delivers them to the ER for insertion2,3,4. The mechanism that permits TRC40 to find and capture its TA protein cargos effectively in a highly crowded cytosol is unknown. Here we identify a conserved three-protein complex composed of Bat3, TRC35 and Ubl4A that facilitates TA protein capture by TRC40. This Bat3 complex is recruited to ribosomes synthesizing membrane proteins, interacts with the TMDs of newly released TA proteins, and transfers them to TRC40 for targeting. Depletion of the Bat3 complex allows non-TRC40 factors to compete for TA proteins, explaining their mislocalization in the analogous yeast deletion strains5,6,7. Thus, the Bat3 complex acts as a TMD-selective chaperone that effectively channels TA proteins to the TRC40 insertion pathway.

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Acknowledgements

We thank S. Appathurai and M. Downing for technical assistance, Hegde lab members for advice, and J. Weissman and W. Clemons for useful discussions and sharing results before publication. This work was supported by the Intramural Research Program of the National Institutes of Health (R.S.H.) and Edward Mallinckrodt Jr Foundation (R.J.K.).

Author information

Affiliations

  1. Cell Biology and Metabolism Program, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA

    • Malaiyalam Mariappan
    • , Xingzhe Li
    • , Sandra Stefanovic
    • , Ajay Sharma
    •  & Ramanujan S. Hegde
  2. School of Basic Medical Sciences, Peking University, 100191 Beijing, China

    • Xingzhe Li
  3. Department of Biochemistry and Molecular Biology, 929 East 57th Street, University of Chicago, Chicago, Illinois 60637, USA

    • Agnieszka Mateja
    •  & Robert J. Keenan

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Contributions

M.M. performed most of the functional analyses of the Bat3 complex, with significant contributions from X.L. during the initial phase of this study. S.S. and R.S.H. developed and characterized the RNC release assay, S.S. initially identified Bat3, and A.S. performed the tRNA-association experiments. A.M. and R.J.K. produced and functionally characterized recombinant proteins, and provided experimental ideas. M.M., X.L., S.S. and R.S.H. analysed data. R.S.H. conceived the project, guided experiments and wrote the paper with input from all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Ramanujan S. Hegde.

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https://doi.org/10.1038/nature09296

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