Wnts grasp the WIF domain of Wnt Inhibitory Factor 1 at two distinct binding sites

Wnts have a structure resembling a hand with “thumb” and “index” fingers that grasp the cysteine rich domains of Frizzled receptors at two distinct binding sites. In the present work we show that the WIF domain of Wnt Inhibitory Factor 1 is also bound by Wnts at two sites. Using C-terminal domains of Wnt5a and Wnt7a and arginine-scanning mutagenesis of the WIF domain we demonstrate that, whereas the N-terminal, lipid-modified “thumb” of Wnts interacts with the alkyl-binding site of the WIF domain, the C-terminal domain of Wnts (Wnt-CTD) binds to a surface on the opposite side of the WIF domain.