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A biphasic pulling force acts on transmembrane helices during translocon-mediated membrane integration

Nature Structural & Molecular Biology volume 19, pages 1018–1022 (2012)Cite this article

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Abstract

Membrane proteins destined for insertion into the inner membrane of bacteria or the endoplasmic reticulum membrane in eukaryotic cells are synthesized by ribosomes bound to the bacterial SecYEG or the homologous eukaryotic Sec61 translocon. During co-translational membrane integration, transmembrane α-helical segments in the nascent chain exit the translocon through a lateral gate that opens toward the surrounding membrane, but the mechanism of lateral exit is not well understood. In particular, little is known about how a transmembrane helix behaves when entering and exiting the translocon. Using translation-arrest peptides from bacterial SecM proteins and from the mammalian Xbp1 protein as force sensors, we show that substantial force is exerted on a transmembrane helix at two distinct points during its transit through the translocon channel, providing direct insight into the dynamics of membrane integration.

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Figure 1: Translation arrest of Lep constructs induced by the M. succiniciproducens and E. coli SecM arrest peptides.
Figure 2: A biphasic pulling force acts on the nascent chain.
Figure 3: Determination of the location of the H segment in the translocon by glycosylation mapping.
Figure 4: Model for membrane integration.

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Acknowledgements

We thank S. Bhushan and P.F. Egea for advice, and C. Lundin for technical assistance. This work was supported by grants from the European Research Council (ERC-2008-AdG 232648), the Swedish Foundation for Strategic Research, the Swedish Research Council, and the Swedish Cancer Foundation to G.v.H.

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Authors and Affiliations

  1. Department of Biochemistry and Biophysics, Center for Biomembrane Research, Stockholm University, Stockholm, Sweden

    Nurzian Ismail, Rickard Hedman, Nina Schiller & Gunnar von Heijne

  2. Science for Life Laboratory, Stockholm University, Solna, Sweden

    Gunnar von Heijne

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  1. Nurzian Ismail
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  2. Rickard Hedman
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  3. Nina Schiller
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  4. Gunnar von Heijne
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Contributions

N.I., R.H. and N.S. contributed to the study design, the experimental work and the writing of the paper. G.v.H. contributed to the study design and the writing of the paper.

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Correspondence to Gunnar von Heijne.

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The authors declare no competing financial interests.

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Supplementary Figures 1–6 and Supplementary Tables 1 and 2 (PDF 18284 kb)

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Ismail, N., Hedman, R., Schiller, N. et al. A biphasic pulling force acts on transmembrane helices during translocon-mediated membrane integration. Nat Struct Mol Biol 19, 1018–1022 (2012). https://doi.org/10.1038/nsmb.2376

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