Small temperature oscillations promote protein crystallization

Abstract

Small temperature oscillations (TOs) are shown to increase the success rates of protein crystallization experiments by enhancing protein nucleation and by inducing the formation of larger crystals. This effect was initially found when we accidentally used a defective crystallization incubator and it is now confirmed for the crystallization of egg-white lysozyme at 14 and 20 degrees C, and also glucose isomerase at 20 degrees C, both under experimental conditions close to the nucleation zone of the proteins' phase diagram. Measurements of the nucleation times at constant lysozyme and precipitant concentrations show that the nucleation promoting effect is due to favourable crystallization pathways induced by TOs. The imposed TOs were +/- 1.0 degrees C during complete cycles of 20 min. X-Ray diffraction studies show worst and more disperse resolution limits when the lysozyme crystals are grown at constant temperature (2.05 +/- 0.51 angstrom without TOs, and 1.79 +/- 0.15 angstrom with TOs).