Sutton B J, Artymiuk P J, Cordero-Borboa A E, Little C, Phillips D C, Waley S G
Department of Zoology, Oxford, U.K.
Biochem J. 1987 Nov 15;248(1):181-8. doi: 10.1042/bj2480181.
Crystals of beta-lactamase II (EC 3.5.2.6., 'penicillinase') from Bacillus cereus were grown with Cd(II) in place of the natural Zn(II) cofactor and stabilized by cross-linking with glutaraldehyde. Their space group is C2, the cell dimensions are a = 5.44 nm, b = 6.38 nm, c = 7.09 nm and beta = 93.6 degrees, and there is one molecule in the asymmetric unit. Diffraction data were collected from cross-linked crystals of the Cd(II)-enzyme, the apoenzyme and six heavy-atom derivatives. The electron-density map calculated at 0.35 nm resolution reveals the essential Cd(II) ion surrounded by three histidine residues and one cysteine residue. The position of a glutamic acid residue, modification of which destroys activity [Little, Emanuel, Gagnon & Waley (1986) Biochem. J. 233, 465-469], suggests the probable location of the active site of the enzyme. Two minor Cd(II) sites not essential for activity were also located. The structure of the apoenzyme at this resolution appears to differ from that of the Cd(II)-enzyme only in the orientation of two of the histidine residues and the cysteine residue that surround the metal ion.
蜡样芽孢杆菌β-内酰胺酶II（EC 3.5.2.6，“青霉素酶”）的晶体在生长时用Cd(II)取代了天然的Zn(II)辅因子，并通过与戊二醛交联进行稳定化处理。其空间群为C2，晶胞参数为a = 5.44 nm，b = 6.38 nm，c = 7.09 nm，β = 93.6°，不对称单元中有一个分子。从Cd(II) - 酶、脱辅基酶和六种重原子衍生物的交联晶体收集了衍射数据。在0.35 nm分辨率下计算得到的电子密度图显示，必需的Cd(II)离子被三个组氨酸残基和一个半胱氨酸残基包围。一个谷氨酸残基的位置，对其进行修饰会破坏活性[利特尔、伊曼纽尔、加尼翁和韦利（1986年）《生物化学杂志》233卷，465 - 469页]，这表明了该酶活性位点的可能位置。还定位了两个对活性非必需的次要Cd(II)位点。在此分辨率下，脱辅基酶的结构似乎与Cd(II) - 酶的结构仅在围绕金属离子的两个组氨酸残基和半胱氨酸残基的取向上有所不同。
