Structural Characterization of Partially Disordered Human Chibby: Insights into Its Function in the Wnt-Signaling Pathway

摘要

The Wnt/β-catenin signaling pathway is critical to embryonic development as well as adult tissuenregeneration. Dysregulation of this pathway can lead to a variety of human diseases, in particular cancers.nChibby (Cby), a small and highly conserved protein, plays an antagonistic role inWnt signaling by inhibitingnthe binding of β-catenin to Tcf/Lef family proteins, a protein interaction that is essential for thentranscriptional activation of Wnt target genes. Cby is also involved in regulating intracellular distributionnof β-catenin. Phosphorylated Cby forms a ternary complex with 14-3-3 protein and β-catenin, facilitating thenexport of β-catenin from the nucleus. On the other hand, the antagonistic function of Cby is inhibited uponnbinding to thyroid cancer-1 (TC-1). To dissect the structure-function relationship of Cby, we have usednNMR spectroscopy, ESI-MS, CD, and DLS to extensively characterize the structure of human Cby. Ournresults show that the 126-residue Cby is partially disordered under nondenaturing conditions. While thenN-terminal portion of the protein is predominantly unstructured in solution, the C-terminal half of Cbynadopts a coiled-coil structure through self-association. Initial data for the binding studies of Cby to 14-3-3ζn(one of the isoforms in the 14-3-3 family) and TC-1 via these two distinct structural modules have also beennobtained. It is noteworthy that in a recent large-scale analysis of the intrinsically disordered proteome ofnmouse, a substantial number of disordered proteins are predicted to have coiled-coil motif presence in theirnsequences. The combination of these two molecular recognition features could facilitate disordered Cby innassembling protein complexes via different modes of interaction.