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Signal sequence–independent membrane targeting of ribosomes containing short nascent peptides within the exit tunnel

Nature Structural & Molecular Biology volume 15, pages 494–499 (2008)Cite this article

Abstract

Ribosomes synthesizing inner membrane proteins in Escherichia coli are targeted to the translocon in the plasma membrane by the signal recognition particle (SRP) and the SRP receptor, FtsY. Here we show using a purified system that membrane targeting does not require an exposed signal-anchor sequence, as SRP-dependent targeting takes place with ribosomes containing short nascent peptides, with or without a signal-anchor sequence, within the peptide exit tunnel. Signaling from inside the tunnel involves ribosomal protein L23, which constitutes part of the SRP binding site. When nascent peptides emerge from the ribosome, the targeting complex is maintained with ribosomes exposing a signal-anchor sequence, whereas ribosomes exposing other sequences are released. These results indicate that ribosome–nascent chain complexes containing any nascent peptide within the exit tunnel can enter the SRP targeting pathway to be sorted at the membrane into ribosome-nascent chain complexes that synthesize either membrane or cytosolic proteins.

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Figure 1: Characterization of RNCs.
Figure 2: Affinity of SRP for RNCs with varying nascent peptides.
Figure 3: Affinity of FtsY for SRP complexes with Lep-RNCs.
Figure 4: SRP-dependent binding of RNCs to inverted inner membrane vesicles.
Figure 5: Ribosomal protein L23 and SRP recruitment.

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Acknowledgements

We thank E. Bibi, Weizmann Institute of Science, Rehovot, Israel, and J. Luirink, Free University of Amsterdam, for kindly providing plasmid constructs, E. Deuerling, University of Konstanz, Germany, for providing the E. coli strain lacking protein L23, and A. Tonevitsky, Moscow State University, for the antibody against Ffh. We are grateful to M. Wahl, Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany, for help with preparing Figure 5b, and to A. Böhm, S. Möbitz, C. Schillings and P. Striebeck for valuable technical assistance. The work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.

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  1. Thomas Bornemann and Johannes Jöckel: These authors contributed equally to this work.

Authors and Affiliations

  1. Institute of Molecular Biology, University of Witten/Herdecke, Stockumer Strasse 10, Witten, 55448, Germany

    Thomas Bornemann, Johannes Jöckel & Wolfgang Wintermeyer

  2. Institute of Physical Biochemistry, University of Witten/Herdecke, Stockumer Strasse 10, Witten, 55448, Germany

    Marina V Rodnina

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T.B. and J.J. performed the experiments, M.V.R. and W.W. supervised the work and wrote the manuscript.

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Correspondence to Wolfgang Wintermeyer.

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Bornemann, T., Jöckel, J., Rodnina, M. et al. Signal sequence–independent membrane targeting of ribosomes containing short nascent peptides within the exit tunnel. Nat Struct Mol Biol 15, 494–499 (2008). https://doi.org/10.1038/nsmb.1402

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