Effect of Pressure on the Crystallization of Proteins

Abstract

Crystals of thaumatin and lysozyme from turkey and hen egg-white have been prepared under hydrostatic pressures in the 0.1-220 MPa range in batch at 20°C in agarose gel. For the three proteins, the number of crystals increases with pressure. For thaumatin and hen lysozyme, crystal length decreases while for turkey lysozyme it increases. The solubility of the first protein decreases, whereas the solubility of both lysozymes increases. In all cases, the relationship between solubility and pressure is linear. The crystallization volume ΔV is -11 cm³ mol⁻¹ for thaumatin, +15 cm³ mol⁻¹ for turkey lysozyme, and +3 cm³ mol⁻¹ for hen lysozyme. For the lysozymes, the values are explained by pressure-dependent conformational changes. The crystals have been analyzed by x-ray diffraction methods. Independently of pressure, the crystals of each protein belong to the same space group. Crystal mosaicity has also been determined. The quality of the lysozyme crystals deteriorates as pressure increases, however thaumatin crystals become more homogeneous. The first result correlates with the apparition of cleavages oriented perpendicularly to the crystal’s c axis. The second one is interpreted by a gradual selection of well-formed nuclei. A potential application of pressure for the preparation of high quality protein crystals is discussed in the light of these results.