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. Also provided are methods of using the compositions.
