Virus And Protein Crystallization Under Hypergravity

One small RNA plant virus and three monomeric and small molecular mass proteins (M-r = 14500-22200) were crystallized in a centrifuge at gravity levels between 1000 and 22000 g under conditions where controls at unit gravity are soluble. Solubility measurements indicate that all crystals have grown in solutions that are metastable, i.e., insufficiently supersaturated to nucleate under normal conditions. Upon centrifugation, particle sedimentation generates a concentration gradient. At highest local concentration, supersaturation is shifted beyond supersolubility and the critical driving force required for nucleation is overcome. A simple procedure has been implemented for sample microvolumes. The habit of protein crystals grown under hypergravity diverges from that of reference crystals but their unit cells are unchanged. Centrifugation is applicable to the crystallization of dilute samples of biological particles with a wide range of sizes, from large viruses to small proteins. It provides a means to control the onset of nucleation and in some cases to accelerate crystal growth.