Figure 6. CaMKII can directly phosphorylate β-catenin.

(A) Amino acid sequence comparison of Gallus gallus and human β-catenin. Dashes indicate conserved residues. Boldface / underline indicates putative CaMKII binding sites (LXXLL) and CaMKII phosphorylation sites (RXXT/S) identified in silico. (B–D) SDS-PAGE and autoradiography of purified phosphoproteins labeled with [γ³²P]-ATP by CaMKII. Reactions contained the respective purified proteins as indicated. (B) CaMKII can phosphorylate the known target protein thrombin-cleaved D52 and purified human β-catenin. (C) CaMKII phosphorylation of wild-type β-catenin or β-catenin constructs harboring one of four mutations in putative phosphorylation sites, as indicated. (D) CaMKII phosphorylation of wild-type β-catenin and a β-catenin construct harboring a triple mutation of the CaMKII phosphorylation sites as indicated. For all three experiments, reactions that lack activated CaMKII instead contain unactivated CaMKII prepared in the absence of calcium and calmodulin. The β-catenin doublet in (C) and (D) represents β-catenin with an intact (upper band) or cleaved 4.4kDa His-tag sequence (lower band). For all experiments, lanes contained equimolar levels of β-catenin.