eLife (Jun 2019)

Structural and mutational analysis of the ribosome-arresting human XBP1u

  • Vivekanandan Shanmuganathan,
  • Nina Schiller,
  • Anastasia Magoulopoulou,
  • Jingdong Cheng,
  • Katharina Braunger,
  • Florian Cymer,
  • Otto Berninghausen,
  • Birgitta Beatrix,
  • Kenji Kohno,
  • Gunnar von Heijne,
  • Roland Beckmann

DOI
https://doi.org/10.7554/eLife.46267
Journal volume & issue
Vol. 8

Abstract

Read online

XBP1u, a central component of the unfolded protein response (UPR), is a mammalian protein containing a functionally critical translational arrest peptide (AP). Here, we present a 3 Å cryo-EM structure of the stalled human XBP1u AP. It forms a unique turn in the ribosomal exit tunnel proximal to the peptidyl transferase center where it causes a subtle distortion, thereby explaining the temporary translational arrest induced by XBP1u. During ribosomal pausing the hydrophobic region 2 (HR2) of XBP1u is recognized by SRP, but fails to efficiently gate the Sec61 translocon. An exhaustive mutagenesis scan of the XBP1u AP revealed that only 8 out of 20 mutagenized positions are optimal; in the remaining 12 positions, we identify 55 different mutations increase the level of translational arrest. Thus, the wildtype XBP1u AP induces only an intermediate level of translational arrest, allowing efficient targeting by SRP without activating the Sec61 channel.

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