On the Mixing of Protein Crystallization Cocktails

HOWARD, EDUARDO I; FERNANDEZ, JOSE MIGUEL; GARCIA-RUIZ, JUAN MANUEL

CRYSTAL GROWTH & DESIGN

AMER CHEMICAL SOC

Año: 2009 vol. 9 p. 2707 - 2712

1528-7483

The first step in the implementation of protein crystallisation experiments by batch andvapour diffusion techniques is the mixing of the solution of the protein and the solutionof the precipitating agent to form a drop. It is demonstrated by optical microscopy andby Mach-Zhender interferometry that depending of the relative values of the propertiesof both solutions and on the sequence of mixing (protein over precipitant solution orvice versa) complex but well-defined fluid patterns occur. The formation of thesepatterns is governed by phenomena such as density driven flow, Rayleigh-Taylorinstability, salt fingering, diffusive-reactive and double diffusive instabilities. Theformation of local supersaturation maxima and minima in the crystallization drop due tothese phenomena explain why and how the protocol of mixing may affect thecrystallization results. As a practical application of this study, it is recommended toperform active mixing when seeking for reproducibility while avoiding active mixingwhen seeking for a more complex and extensive screening of the crystallisation space.