Structure and functional properties of Norrin mimic Wnt for signalling with Frizzled4, Lrp5/6, and proteoglycan

Elife. 2015 Jul 9;4:e06554. doi: 10.7554/eLife.06554.

Abstract

Wnt signalling regulates multiple processes including angiogenesis, inflammation, and tumorigenesis. Norrin (Norrie Disease Protein) is a cystine-knot like growth factor. Although unrelated to Wnt, Norrin activates the Wnt/β-catenin pathway. Signal complex formation involves Frizzled4 (Fz4), low-density lipoprotein receptor related protein 5/6 (Lrp5/6), Tetraspanin-12 and glycosaminoglycans (GAGs). Here, we report crystallographic and small-angle X-ray scattering analyses of Norrin in complex with Fz4 cysteine-rich domain (Fz4CRD), of this complex bound with GAG analogues, and of unliganded Norrin and Fz4CRD. Our structural, biophysical and cellular data, map Fz4 and putative Lrp5/6 binding sites to distinct patches on Norrin, and reveal a GAG binding site spanning Norrin and Fz4CRD. These results explain numerous disease-associated mutations. Comparison with the Xenopus Wnt8-mouse Fz8CRD complex reveals Norrin mimics Wnt for Frizzled recognition. The production and characterization of wild-type and mutant Norrins reported here open new avenues for the development of therapeutics to combat abnormal Norrin/Wnt signalling.

Keywords: Wnt signalling; angiogenesis; biophysics; blood brain barrier; crystal structure; cystine-knot growth factor; developmental biology; human; mouse; retinal disease; stem cells; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Crystallography, X-Ray
  • Eye Proteins / chemistry*
  • Eye Proteins / genetics
  • Eye Proteins / metabolism
  • Frizzled Receptors / chemistry*
  • Frizzled Receptors / metabolism
  • Humans
  • Low Density Lipoprotein Receptor-Related Protein-5 / metabolism
  • Low Density Lipoprotein Receptor-Related Protein-6 / metabolism
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Protein Conformation
  • Proteoglycans / chemistry*
  • Proteoglycans / metabolism
  • Scattering, Small Angle

Substances

  • Eye Proteins
  • FZD4 protein, human
  • Frizzled Receptors
  • Low Density Lipoprotein Receptor-Related Protein-5
  • Low Density Lipoprotein Receptor-Related Protein-6
  • Lrp5 protein, mouse
  • Lrp6 protein, mouse
  • Mutant Proteins
  • NDP protein, human
  • Nerve Tissue Proteins
  • Proteoglycans