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 Ni 2+ , Mn 2+ , Co 2+ , and Yb 3+ 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 Mg 2+ and Ca 2+ 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 MgCl 2 , CaCl 2 , NiCl 2 , MnCl 2 , CoCl 2 , and YbCl 3 , have been determined by X‐ray crystallography at 1.58 Å resolution. The crystals grown in these salts have an identical space group, P 4 3 2 1 2. The molecules show no conformational changes, irrespective of the salts used. Ni 2+ and Co 2+ binding to the Oδ atom of Asp52 in the active site at 1.98 and 2.02 Å, respectively, and Yb 3+ 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 Mn 2+ , Mg 2+ , and Ca 2+ have not been found from different Fourier electron density maps. The Ni 2+ and Co 2+ ions bind to the Oδ atom of Asp52 at almost the same position, while the Yb 3+ ion takes a different position from the Ni 2+ and Co 2+ 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