text: For GSK3 to be a highly effective kinase on a substrate, pre-phosphorylation is not enough. There is one additional requirement: Similar to the mitogen-activated protein kinases (MAPKs), substrates need to associate with this enzyme through high-affinity docking motifs. β-Catenin contains no such motifs, but a special protein does: axin. What is more, its GSK3 docking motif is directly adjacent to a β-catenin binding motif. This way, axin acts as a true scaffold protein, bringing an enzyme (GSK3) together with its substrate (β-catenin) into close physical proximity.
  But even axin does not act alone. Through its N-terminal regulator of G-protein signaling (RGS) domain, it recruits the adenomatous polyposis coli (APC) protein. APC is like a huge "Christmas tree": with a multitude of β-catenin binding motifs (one APC molecule alone possesses 11 such motifs ), it may collect as many β-catenin molecules as possible. APC can interact with multiple axin molecules at the same time as it has three SAMP motifs (Ser-Ala-Met-Pro) to bind the RGS domains found in axin. In addition, axin also has the potential to oligomerize through its C-terminal DIX domain. The result is a huge, multimeric protein assembly dedicated to β-catenin phosphorylation. This complex is usually called the beta-catenin destruction complex, although it is distinct from the proteosome machinery actually responsible for β-catenin degradation. It only marks β-catenin molecules for subsequent destruction.