Provided is a composition comprising a peptide comprising amino acids and/or amino acid analogs comprising a continuous sequence of a sclerostin fragment comprising Tyr43 or Tyr213. Also provided is a composition comprising a peptide comprising less than about 75 amino acids and/or amino acid analogs including an amino acid or amino acid analog capable of being sulfated, where the composition is capable of inhibiting sclerostin binding to an LRP. Further provided is a composition comprising a peptide comprising less than about 75 amino acids and/or amino acid analogs including an amino acid or amino acid analog capable of being post-translationally sulfated, where the composition is capable of inhibiting binding of a protein ligand comprising a sulfation site to its binding partner. Additionally provided is a method of enhancing a Wnt signaling pathway comprising contacting an LRP5/6 receptor in the Wnt signaling pathway with either of the above-described compositions that comprise a sequence of a sclerostin fragment or is capable of inhibiting sclerostin binding to an LRP, where the tyrosine or tyrosine analog is not sulfated, in a manner sufficient to enhance the Wnt signaling pathway. Further provided is a method of treating a subject having a disease exacerbated by inhibition of a Wnt signaling pathway comprising administering either of the above-described compositions that comprise a sequence of a sclerostin fragment or is capable of inhibiting sclerostin binding to an LRP, where the tyrosine or tyrosine analog is not sulfated, to the subject in a manner sufficient to reduce the inhibition of the Wnt signaling pathway. Also, a method of inhibiting binding of a protein ligand comprising a sulfation site to its binding partner is provided. The method comprises adding the above-described composition that is capable of inhibiting binding of a protein ligand to its binding partner to the protein ligand and its binding partner in a manner sufficient to inhibit bindin
