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Importin-α-16 is a translocon-associated protein involved in sorting membrane proteins to the nuclear envelope

Nature Structural & Molecular Biology volume 13, pages 500–508 (2006)Cite this article

Abstract

A viral inner nuclear membrane–sorting motif sequence (INM-SM) was used to identify proteins that recognize integral membrane proteins destined for the INM. Herein we describe importin-α-16, a membrane-associated isoform of Spodoptera frugiperda importin-α that contains the C-terminal amino acid residues comprising armadillo helical-repeat domains 7–10. In the endoplasmic reticulum (ER) membrane, importin-α-16 is adjacent to the translocon protein Sec61α. Importin-α-16 cross-links to the INM-SM sequence as it emerges from the ribosomal tunnel and remains adjacent to the INM-SM after INM-SM integration into the ER membrane and release from the translocon. Cross-linking results suggest that importin-α-16 discriminates between INM- and non–INM-directed proteins. Thus, it seems that during and after cotranslational membrane integration, importin-α-16 is involved in the trafficking of integral membrane proteins to the INM.

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Figure 1: SMC cross-links to two cellular proteins, p10 and p25.
Figure 2: E26 shares epitopes with p10.
Figure 3: C2301–454 cross-links with the SMC.
Figure 4: C2301–454 is a translocon-associated protein that has substrate specificity for SMC.
Figure 5: Primer-extension analysis.
Figure 6: C2 encodes Sf9 importin-α.
Figure 7: Model of importin-α-16 involvement in membrane protein trafficking to the INM.

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Acknowledgements

We thank C. Gross, Vertex Pharmaceuticals, for the Sf9 cDNA expression library and Y. Miao and Y. Shao for excellent technical assistance. J. Sacchettini and C. Savva were especially helpful in our efforts to model C2 and provide convincing evidence that C2 is a member of the importin-α family of proteins. BLAST computation was performed at the Swiss Institute of Bioinformatics using the BLAST network service. This article was submitted by S.S. in partial fulfillment of the Ph.D. degree at Texas A&M University. This work was supported by US National Institutes of Health RO1 grant GM26494 (to A.E.J.), the Robert A. Welch Foundation (to A.E.J.) and Texas Agricultural Experiment Station Project grant TEXO-08078 (to M.D.S.).

Author information

Authors and Affiliations

  1. Departments of Biochemistry and Biophysics, Texas A&M University, 77843, Texas, USA

    Suraj Saksena, Max D Summers & Arthur E Johnson

  2. Department of Biology, Texas A&M University, 77843, Texas, USA

    Max D Summers & Jared K Burks

  3. Department of Entomology, Texas A&M University, 77843, Texas, USA

    Max D Summers & Sharon C Braunagel

  4. Texas Agricultural Experiment Station, Texas A&M University, 77843, Texas, USA

    Max D Summers & Sharon C Braunagel

  5. Department of Chemistry, Texas A&M University System Health Science Center, College Station, 77843, Texas, USA

    Arthur E Johnson

  6. Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, 77843, Texas, USA

    Arthur E Johnson

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Correspondence to Sharon C Braunagel.

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Supplementary information

Supplementary Fig. 1

Annotated sequence of C2 (PDF 110 kb)

Supplementary Fig. 2

C2301–454 cross-links with the SMC (PDF 998 kb)

Supplementary Fig. 3

Comparison of the sequence of the viral protein E26 with cellular importin-α proteins (PDF 99 kb)

Supplementary Discussion (PDF 119 kb)

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Saksena, S., Summers, M., Burks, J. et al. Importin-α-16 is a translocon-associated protein involved in sorting membrane proteins to the nuclear envelope. Nat Struct Mol Biol 13, 500–508 (2006). https://doi.org/10.1038/nsmb1098

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