Structural details at active site of hen egg white lysozyme with di- and trivalent metal ions

Metal binding to lysozyme has recieved wide interest. In particular, it is interesting that Ni2+, Mn2+, Co2+, and Yb3+ chloride salts induce an increase in the solubility of the tetragonal form in crystals of hen egg white lysozyme at high salt concentration, but that Mg2+ and Ca2+ chloride salts do not. To investigate the interactions of the di- and trivalent metal ions with the active site of lysozyme and compare the effects of the di- and trivalent metal ions on molecular conformation of lysozyme based on the structural analysis, the crystal structures of hen egg white lysozyme grown at pH 4.6, in the presence of 0.5 M MgCl2, CaCl2, NiCl2, MnCl2, CoCl2, and YbCl3, have been determined by X-ray crystallography at 1.58 angstrom resolution. The crystals grown in these salts have an identical space group, P4(3)2(1)2. The molecules show no conformational changes, irrespective of the salts used. Ni2+ and Co2+ binding to the 0 delta atom of Asp52 in the active site at 1.98 and 2.02 angstrom, respectively, and Yb3+ binding to both the O delta atom of Asp52 and the O delta 1 atom of Asn46 at 2.25 angstrom have been identified. The binding sites of Mn2+, Mg2+, and Ca2+ have not been found from different Fourier electron density maps. The Ni2+ and Co2+ ions bind to the O delta atom of Asp52 at almost the same position, while the Yb3+ ion takes a different position from the Ni2+ and Co2+ ions. On the other hand, the anion Cl-, interacting with the O eta atom of Tyr23 at a site of about 2.90 angstrom, has also been determinedfor each crystal. (C) 2005 Wiley Periodicals, Inc.