A method of modifying a test nuclear receptor (NR) polypeptide is disclosed. The method provides a test NR polypeptide sequence having a characteristic that is targeted for modification; aligning the test NR polypeptide sequence with at least one reference NR polypeptide sequence for which an X-ray structure is available; building a three-dimensional model for the test NR polypeptide using the three-dimensional coordinates of the X-ray structure(s) of at least one reference polypeptide and its sequence alignment with the test NR polypeptide sequence; examining the three-dimensional model of the test NR polypeptide sequence for characteristic differences with the reference polypeptide; and mutating at least one amino acid residue in the test NR polypeptide sequence at a characteristic difference, whereby the test NR polypeptide is modified.