Abstract

Purity is an important factor in producing good crystals. Macromolecular contaminants and micro-heterogeneities that are present within a protein batch poison the faces of growing crystals and alter the crystal parking. Although macromolecular purity is thought to be essential for the growth of flawless protein crystals, only a few studies have investigated how contaminants alter or can vary in some way the crystallisation process, and crystal quality. Likewise, the outcome of a crystallisation process may vary with the crystallisation method. In this talk, I will show some examples of how these two variables affect crystallogenesis: aspartyl-tRNA synthetase from the eubacterium Thermus thermophilus, cytochrome C from bovine’s heart and Ferritin from horse’s spleen and other proteins. Minute amounts of protein impurities alter to different extents the growth of each crystal form of asparthyl-tRNA synthetase and, they affect the presence of the isoforms of high quality crystals of cytochrome C. I will also discuss the role of additives (precipitant solutions) and crystallisation method for the control of crystal morphology of Ferritin. Finally I will show that after removing the impurities, the best crystals are only obtained when the crystallizing solution is either enclosed in capillaries or immobilised in agarose gel or controlling the kinetics by applying a direct current/voltage during the crystallisation process. In these two environments convection is reduced compared to that existing in an unconstrained solution, and at the same time gel is working as a filter of impurities. In this seminar, the advantages and disadvantages of having impurities, mixture of precipitating solutions, and the crystal growth methods for applications in protein crystallisation for high quality crystal obtaining, are revised.