Li Shu Jie
Department of Biophysics, College of Physics Science, Nankai University, Tianjin 300071, People's Republic of China.
Biopolymers. 2006 Feb 5;81(2):74-80. doi: 10.1002/bip.20367.
Metal binding to lysozyme has received 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 A 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 Odelta atom of Asp52 in the active site at 1.98 and 2.02 A, respectively, and Yb3+ binding to both the Odelta atom of Asp52 and the Odelta1 atom of Asn46 at 2.25 A 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 Odelta 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 Oeta atom of Tyr23 at a site of about 2.90 A, has also been determined for each crystal.
金属与溶菌酶的结合已引起广泛关注。特别值得注意的是，在高盐浓度下，Ni2+、Mn2+、Co2+和Yb3+的氯化物盐会使鸡蛋清溶菌酶晶体中四方晶型的溶解度增加，但Mg2+和Ca2+的氯化物盐却不会。为了研究二价和三价金属离子与溶菌酶活性位点的相互作用，并基于结构分析比较二价和三价金属离子对溶菌酶分子构象的影响，我们通过X射线晶体学在1.58 Å分辨率下测定了在pH 4.6、存在0.5 M MgCl2、CaCl2、NiCl2、MnCl2、CoCl2和YbCl3条件下生长的鸡蛋清溶菌酶的晶体结构。在这些盐中生长的晶体具有相同的空间群P4(3)2(1)。无论使用何种盐，分子均未显示出构象变化。已确定Ni2+和Co2+分别以1.98 Å和2.02 Å的距离与活性位点中Asp52的Oδ原子结合，Yb3+以2.25 Å的距离与Asp52的Oδ原子和Asn46的Oδ1原子结合。从不同的傅里叶电子密度图中未发现Mn2+、Mg2+和Ca2+的结合位点。Ni2+和Co2+离子在几乎相同的位置与Asp52的Oδ原子结合，而Yb3+离子与Ni2+和Co2+离子的位置不同。另一方面，还确定了每种晶体中与Tyr23的Oη原子在约2.90 Å位点相互作用的阴离子Cl-。
