A novel technique for containerless protein crystallization

Heterogeneous nucleation, which is often detrimental to the production of suitable crystals for X-ray diffraction, can be induced by the contact of a crystallization sample with the walls of its supporting vessel. A novel method for creating a 'containerless' environment for the growth of protein crystals is described. Contact between the container walls and a crystallization drop is eliminated by suspending the drop between two oils of different density: one of higher and the other of lower density than that of water and the common precipitating agents. A number of proteins were crystallized in 2-10 microliters drops using this procedure. It was found that the number of crystals obtained in such suspended drops was reduced significantly compared with the number of crystals obtained in trials where the crystallization drop was situated at the bottom of a vial under a single layer of oil. This method has potential in controlling heterogeneous nucleation.