 Although one molecule of axin only contains a single β-catenin recruitment motif, its partner the Adenomatous Polyposis Coli (APC) protein contains 11 such motifs in tandem arrangement per protomer, thus capable to interact with several β-catenin molecules at once.Since the surface of the ARM domain can typically accommodate only one peptide motif at any given time, all these proteins compete for the same cellular pool of β-catenin molecules.This competition is the key to understand how the Wnt signaling pathway works.