The phosphorylation of the 20 aa repeats in APC results in an increase in affinity for beta-catenin (Ha et al., 2004, Xing et al., 2004; Liu et al., 2006). The binding site of phospho -(20 aa) APC on beta-catenin overlaps the binding site of Axin on beta catenin. In addition, phosphorylated APC prevents the association of Axin with beta-catenin (Ha et al., 2004, Xing et al., 2004). In this model, phosphorylated APC may compete with Axin for beta-catenin binding, resulting in dissociation of the Axin:beta-catenin interaction in the destruction complex (see Kimelman and Xu 2006).
