Structural characterization of partially disordered human Chibby: insights into its function in the Wnt-signaling pathway

Biochemistry. 2011 Feb 8;50(5):715-26. doi: 10.1021/bi101236z. Epub 2011 Jan 14.

Abstract

The Wnt/β-catenin signaling pathway is critical to embryonic development as well as adult tissue regeneration. Dysregulation of this pathway can lead to a variety of human diseases, in particular cancers. Chibby (Cby), a small and highly conserved protein, plays an antagonistic role in Wnt signaling by inhibiting the binding of β-catenin to Tcf/Lef family proteins, a protein interaction that is essential for the transcriptional activation of Wnt target genes. Cby is also involved in regulating intracellular distribution of β-catenin. Phosphorylated Cby forms a ternary complex with 14-3-3 protein and β-catenin, facilitating the export of β-catenin from the nucleus. On the other hand, the antagonistic function of Cby is inhibited upon binding to thyroid cancer-1 (TC-1). To dissect the structure-function relationship of Cby, we have used NMR spectroscopy, ESI-MS, CD, and DLS to extensively characterize the structure of human Cby. Our results show that the 126-residue Cby is partially disordered under nondenaturing conditions. While the N-terminal portion of the protein is predominantly unstructured in solution, the C-terminal half of Cby adopts a coiled-coil structure through self-association. Initial data for the binding studies of Cby to 14-3-3ζ (one of the isoforms in the 14-3-3 family) and TC-1 via these two distinct structural modules have also been obtained. It is noteworthy that in a recent large-scale analysis of the intrinsically disordered proteome of mouse, a substantial number of disordered proteins are predicted to have coiled-coil motif presence in their sequences. The combination of these two molecular recognition features could facilitate disordered Cby in assembling protein complexes via different modes of interaction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Humans
  • Molecular Conformation
  • Molecular Sequence Data
  • Nuclear Proteins / chemistry*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Binding
  • Protein Structure, Tertiary
  • Signal Transduction*
  • Wnt Proteins / genetics
  • Wnt Proteins / metabolism*

Substances

  • CBY1 protein, human
  • Carrier Proteins
  • Nuclear Proteins
  • Wnt Proteins