Dickkopf-related proteins are cysteine-rich secretory proteins and highly conserved inhibitors of the canonical Wnt signaling pathway, which play key roles in many essential biological processes. The C-terminal domain is described as two subdomains, each consisting of three anti-parallel beta-strands that are connected by a long loop which contains a short alpha-helix. This domain is strongly conserved in Dkk1, Dkk2 and Dkk4, and directly contacts LRP6. This entry represents the second subdomain [1-4]. In Dkk3 these residues differ and is consistent with studies indicating that Dkk3 is a divergent family member that does not inhibit Wnt signalling [4]. This domain share significant sequence similarity to the colipase fold.

1: Structural insight into the mechanisms of Wnt signaling antagonism by Dkk. Chen L, Wang K, Shao Y, Huang J, Li X, Shan J, Wu D, Zheng JJ; J Biol Chem. 2008;283:23364-23370. PMID:18524778

2: Structural basis of Wnt signaling inhibition by Dickkopf binding to LRP5/6. Ahn VE, Chu ML, Choi HJ, Tran D, Abo A, Weis WI; Dev Cell. 2011;21:862-873. PMID:22000856

3: Crystal structures of the extracellular domain of LRP6 and its complex with DKK1. Cheng Z, Biechele T, Wei Z, Morrone S, Moon RT, Wang L, Xu W; Nat Struct Mol Biol. 2011;18:1204-1210. PMID:21984209

4: Structure of the Dual-Mode Wnt Regulator Kremen1 and Insight into Ternary Complex Formation with LRP6 and Dickkopf. Zebisch M, Jackson VA, Zhao Y, Jones EY; Structure. 2016;24:1599-1605. PMID:27524201