Protein crystallization on polymeric film surfaces

Polymeric films containing ionizable groups, such as sulfonated polystyrene , cross-linked gelatin films with adsorbed poly-L-lysine or entrapped poly- L-aspartate and silk fibroin with entrapped poly-L-lysine or poly-L-asparta te, have been tested as heterogeneous nucleant surfaces for proteins. Conca navalin A from jack bean and chicken egg-white lysozyme were used as models . It was found that the crystallization of concanavalin A by the vapor diff usion technique, is strongly influenced by the presence of ionizable groups on the film surface. Both the induction time and protein concentration nec essary for the crystal nucleation decrease whereas the nucleation density i ncreases on going from the reference siliconized cover slip to the uncharge d polymeric surfaces and even more to the charged ones. Non-specific attrac tive and local interactions between the protein and the film surface might promote molecular collisions and the clustering with the due symmetry for t he formation of the crystal nuclei. The results suggest that the studied po lymeric film surfaces could be particularly useful for the crystallization of proteins from solutions at low starting concentration, thus using small quantities of protein, and for proteins with very long crystallization time . (C) 2001 Elsevier Science B.V. All rights reserved.