CADMIUM-INDUCED CRYSTALLIZATION OF PROTEINS - II - CRYSTALLIZATION OFTHE SALMONELLA-TYPHIMURIUM HISTIDINE-BINDING PROTEIN IN COMPLEX WITH L-HISTIDINE, L-ARGININE, OR L-LYSINE

To further investigate favorable effects of divalent cations on the fo rmation of protein crystals, three complexes of Salmonella typhimurium histidine-binding protein were crystallized with varying concentratio ns of cadmium salts. For each of the three histidine-binding protein c omplexes, cadmium cations were found to promote or improve crystalliza tion. The optimal cadmium concentration is ligand specific and falls w ithin a narrow concentration range. In each case, crystals grown in th e presence of cadmium diffract to better than 2.0 Angstrom resolution and belong to the orthorhombic space group P2(1)2(1)2(1). From our res ults and from the analysis of cadmium sites in well-refined protein st ructures, we propose that cadmium addition provides a generally useful technique to modify crystal morphology and to improve diffraction qua lity.