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

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Abstract
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 Å resolution. The crystals grown in these salts have an identical space group, P43212. The molecules show no conformational changes, irrespective of the salts used. Ni2+ and Co2+ binding to the Oδ atom of Asp52 in the active site at 1.98 and 2.02 Å, respectively, and Yb3+ binding to both the Oδ atom of Asp52 and the Oδ1 atom of Asn46 at 2.25 Å 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 Oδ 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 Oη atom of Tyr23 at a site of about 2.90 Å, has also been determined for each crystal. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 74-80, 2006 This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com