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Slow translocon gating causes cytosolic exposure of transmembrane and lumenal domains during membrane protein integration

Nature Structural & Molecular Biology volume 13, pages 930–936 (2006)Cite this article

Abstract

Integral membrane proteins are cotranslationally inserted into the endoplasmic reticulum via the protein translocation channel, or translocon, which mediates the transport of lumenal domains, retention of cytosolic domains and integration of transmembrane spans into the phospholipid bilayer. Upon translocon binding, transmembrane spans interact with a lateral gate, which regulates access to membrane phospholipids, and a lumenal gate, which controls the translocation of soluble domains. We analyzed the in vivo kinetics of integration of model membrane proteins in Saccharomyces cerevisiae using ubiquitin translocation assay reporters. Our findings indicate that the conformational changes in the translocon that permit opening of the lumenal and lateral channel gates occur less rapidly than elongation of the nascent polypeptide. Transmembrane spans and lumenal domains are therefore exposed to the cytosol during integration of a polytopic membrane protein, which may pose a challenge to the fidelity of membrane protein integration.

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Figure 1: Kinetics of Dap2 reporter integration.
Figure 2: Translocon gating by Suc2 RNCs and Dap2 RNCs.
Figure 3: Translocon gating by a polytopic membrane protein.
Figure 4: Effect of loop insertions on UTA reporter cleavage.
Figure 5: Targeting of membrane proteins by the Suc2p signal sequence.
Figure 6: Cytosolic exposure of TM spans and lumenal domains during in vivo integration of a polytopic membrane protein.

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Acknowledgements

We thank J. Brown (University of Newcastle) for providing plasmid pJEY117 and C. Stirling (University of Manchester) for providing yeast strains. This work was supported by US National Institutes of Health grant GM35687.

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  1. Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, 01605-2324, Massachusetts, USA

    Zhiliang Cheng & Reid Gilmore

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Correspondence to Reid Gilmore.

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Cheng, Z., Gilmore, R. Slow translocon gating causes cytosolic exposure of transmembrane and lumenal domains during membrane protein integration. Nat Struct Mol Biol 13, 930–936 (2006). https://doi.org/10.1038/nsmb1146

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