Structural effects of monovalent anions on polymorphic lysozyme crystals

Understanding direct salt effects on protein crystal polymorphism is addres sed by comparing different crystal forms (triclinic, monoclinic, tetragonal and orthorhombic) for hen, turkey, bob white quail and human lysozymes. Fo ur new structures of hen egg-white lysozyme are reported: crystals grown in the presence of NapTS diffracted to 1.85 Angstrom, of NaI to 1.6 Angstrom, of NaNO3 to 1.45 Angstrom and of KSCN to 1.63 Angstrom. These new structur es are compared with previously published structures in order to draw a map ping of the surface of different lysozymes interacting with monovalent anio ns, such as nitrate, chloride, iodide, bromide and thiocyanate. An analysis of the structural sites of these anions in the various lysozyme structures is presented. This study shows common anion sites whatever the crystal for m and the chemical nature of anions, while others seem specific to a given geometry and a particular charge environment induced by the crystal packing .