Cell Reports
Volume 18, Issue 1, 3 January 2017, Pages 32-40
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Conformational Freedom of the LRP6 Ectodomain Is Regulated by N-glycosylation and the Binding of the Wnt Antagonist Dkk1

https://doi.org/10.1016/j.celrep.2016.12.017Get rights and content
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Highlights

  • Negative-stain EM reveals that the entire LRP6 ectodomain is flexible

  • Bending angle of the LRP6 ectodomain is regulated by N-glycans located at the hinge

  • 3D structure of LRP6ec/Dkk1 complex is determined by the random conical tilt method

  • Dkk1 binding induces conformational changes in the LRP6 ectodomain

Summary

LDL-receptor-related protein 6 (LRP6) is a single-pass membrane glycoprotein with a large modular ectodomain and forms a higher order signaling platform upon binding Wnt ligands on the cell surface. Although multiple crystal structures are available for fragments of the LRP6 ectodomain, we lack a consensus view on the overall molecular architecture of the full-length LRP6 and its dynamic aspects. Here, we used negative-stain electron microscopy to probe conformational states of the entire ectodomain of LRP6 in solution and found that the four-module ectodomain undergoes a large bending motion hinged at the junction between the second and the third modules. Importantly, the extent of inter-domain motion is modulated by evolutionarily conserved N-glycan chains proximal to the joint. We also found that the LRP6 ectodomain becomes highly compact upon complexation with the Wnt antagonist Dkk1, suggesting a potential role for the ectodomain conformational change in the regulation of receptor oligomerization and signaling.

Keywords

LRP6
Wnt signal
negative-stain electron microscopy
Dkk1
single particle analysis
N-glycosylation
conformational flexibility
receptor ectodomain

Cited by (0)

2

Present address: Graduate Group in Biophysics, MC 2530, University of California, San Francisco, CA 94158-2330, USA

3

Lead Contact