Different mechanisms of Wnt singaling inhibition. In an activated state (uninhibited) a Wnt molecule binds to a Fzd receptor and a co-receptor of the Lrp family. Dkk molecules interact with Krm receptors to form a ternary complex with Lrp co-receptors, thereby removing them from the activation complex. Sclerostin (Scl) has been suggested to function in a similar way, yet its interaction with Lrp5 does not require Krm binding. In contrast, secreted Fzd-related proteins (Sfrps) sequester the activating Wnt ligand to antagonize Wnt signaling.