DKK-1 is a 25.8 kDa secreted protein functioning as antagonist of the canonical Wnt signaling pathway. It is a member of the dickkopf-related protein family characterized by two cysteine-rich domains separated by a linker region. Binding of DKK-1 to the LRP5/6 co-receptor inhibits the interaction with Wnt and by forming a ternary complex with transmembrane Kremen-1 or -2, promotes the internalization of LRP5/6.