Space and terrestrial temperature-induced nucleation and growth of protein single crystals

A method is described for high-quality protein crystal solution growth with the help of localized action of a thermal control field. Two techniques for the nucleation and growth of single crystals of biological macromolecules have been proposed. The first one utilizes a very slow temperature shift at a capillary point where the crystal is to be grown. This allows to suppress an undesirable multiple nucleation. The second technique includes several local rapid temperature changes (a temperature “shock”) forcing the nucleation at the given point.

A mathematical model has been developed and computational investigation has been performed of the processes of protein crystallization from a homogeneous aqueous solution in the crystallization volume. The mathematical model describes crystal nucleation and growth depending on the local supersaturation and temperature as well as heat-and-mass exchange within the entire volume of the solution including the protein crystals.

The temperature was shown to be a factor, capable to initiate and drive the crystallization, and also to influence the nucleation stage and, hence, the protein crystal morphology. This may be useful for obtaining good quality single crystals of biological macromolecules. One or the other technique may be chosen. The stronger the dependence of protein solubility against the temperature, the better chances one has to succeed with any of the approaches, especially with the first one.

The mathematical model developed describes the process of nucleation and growth of protein crystals from solution under the control action of a thermal field based on an intermediate phase concept, the intermediate phase consisting of a mixture of solid and liquid phase fractions. This model was used to calculate an experiment on growing a protein crystal from a homogeneous aqueous solution, with the process of crystal nucleation and growth being acted upon by the precipitant and the thermal field. The calculations showed that this model is adequate to the processes being modeled and can be used for parametric investigations and predictive calculations of protein crystallization processes under thermal control field conditions both under terrestrial and space conditions.

These techniques were successfully tested while growing single crystals of lysozyme, xylanase and human serum albumin (HSA) respectively.