title: Crystallization of recombinant human growth hormone at elevated pressures: pressure effects on PEG-induced volume exclusion interactions.
abstract: Crystallization of recombinant human growth hormone (rhGH) at elevated pressures was investigated in the presence of 6,000 molecular weight poly(ethylene glycol; PEG-6000). Crystallization of rhGH at atmospheric pressure occurred at a protein concentration of 15 mg/mL in 6% PEG-6000. Crystallization did not occur in the same solutions at 250 MPa. In contrast, at a pressure of 250 MPa in the presence of 8% PEG-6000, rhGH readily crystallized from solutions containing 35 mg/mL rhGH, whereas amorphous precipitate formed in the same solutions at atmospheric pressure. Osmotic virial coefficients were determined from static light scattering measurements and combined with a hard-sphere activity coefficient model to predict rhGH activity coefficients as a function of pressure and PEG concentration. Predicted activity coefficients quantitatively matched those determined from equilibrium solubility measurements. The ability to adjust the thermodynamic non-ideality with pressure provides a valuable tool to study protein crystallization in addition to providing a methodology for obtaining crystals at elevated pressures.
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado Center for Pharmaceutical Biotechnology, University of Colorado, Boulder, CO 30309, USA.
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Crisman
authors.forename: Theodore W
authors.initials: TW
authors.lastname: Randolph
mesh_terms: D003460:Crystallization / Q000379:methods; D019382:Human Growth Hormone / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006874:Hydrostatic Pressure; D011092:Polyethylene Glycols / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013678:Technology, Pharmaceutical / Q000379:methods*
chemical_list: D011994:Recombinant Proteins; D019382:Human Growth Hormone; D011092:Polyethylene Glycols