Provided is a protein comprising an antibody binding site that binds to a sulfated epitope of a Wnt pathway protein that is not Wnt5A, Wnt11, or Wnt3a. In one embodiment, the Wnt pathway protein is the Dickkopf1 (Dkk1) protein. Further provided is a composition comprising a peptide less than 75 amino acids or amino acid analogs, the peptide consisting of a fragment of a Wnt pathway protein, such as a Dkk1, wherein the fragment is sulfated.