Investigating the nucleation of protein crystals with hydrostatic pressure

Abstract

Hydrostatic pressure in the 0.1–75 MPa range has been used as a non-invasive tool to studythe crystallization process of the tetragonal crystal form of the protein thaumatin(Mr 22 200). Crystals were prepared within agarose gel and at temperatures in the range from283 to 303 K. The solubility, i.e. the concentration of soluble macromolecules remaining inequilibrium with the crystals, decreases when the pressure increases and when thetemperature decreases. High pressure was used to probe the nucleation behaviour ofthaumatin. The pressure dependence of the nucleation rate leads to an activation volume of−46.5 cm3 mol−1. It is shown that an increase in pressure decreases the enthalpy, the entropy and thefree energy of crystallization of thaumatin. The data are discussed in the lightof the results of crystallographic analyses and of the structure of the protein.