Patent ID: 7824491

Claim:
A method for obtaining a crystal suitable for ligand exchange, comprising incubating a polypeptide at a concentration of about 15-25 mg/ml in a buffered solution, wherein the polypeptide consists of the amino acid sequence of SEQ ID NO: 13 and wherein the buffered solution is at a pH range of 6.0-6.9 and comprises 5-24% polyethylene glycol 5000 monomethyl ether (MPEG 5000), 0-20% polyethylene glycol 2000 dimethyl ether (PEG 2000), 0.1 _M 2-(N-morpholino)ethanesulfonic acid (MES), 0.002 _M Tris (2-carboxyethyl) phosphine hydrochloride (TCEP), and 0.05 to 0.4 M ammonium sulfate.