Fig. 2

Primary and 3D structures of nonbilaterian β-catenins. (A) Overview of phylogeny and structure of β-catenins of early-branching (nonbilaterian) metazoans and ARM6 protein of the unicellular sister taxon, Choanoflagellata. (B) Domain organizations of β-catenin proteins. Metazoan β-catenins show a high degree of conservation of the central region, GSK3β/CK1α phosphorylation sites, and αE-catenin binding sites. At the C-terminus, motif A is conserved in only Bilateria and Cnidaria, whereas motif B is shared among all metazoan lineages, except for Ctenophora. In the choanoflagellate, Salpingoeca rosetta, possible GSK3β phosphorylation sites (S33/T41) were identified. (B) Surface depictions of β-catenin homology structural models were compared with mouse β-catenin. This confirmed that the three crucial arginine residues (dark blue) of nonbilaterians were localized similarly to mouse and Xenopus β-catenins. K556, R551, and K590 of B. mikado β-catenin were located at positions corresponding to mouse β-catenin R474, R469, and K508, but the R582, H578, R612, and Y654 assembly of mouse β-catenin is completely absent in B. mikado β-catenin. Structures visualized using UCSF Chimera software