Jelsch C, Mourey L, Masson J M, Samama J P
Laboratoire de Pharmacologie et de Toxicologie Fondamentales, Toulouse, France.
Proteins. 1993 Aug;16(4):364-83. doi: 10.1002/prot.340160406.
The X-ray structure of Escherichia coli TEM1 beta-lactamase has been refined to a crystallographic R-factor of 16.4% for 22,510 reflections between 5.0 and 1.8 A resolution; 199 water molecules and 1 sulphate ion were included in refinement. Except for the tips of a few solvent-exposed side chains, all protein atoms have clear electron density and refined to an average atomic temperature factor of 11 A2. The estimated coordinates error is 0.17 A. The substrate binding site is located at the interface of the two domains of the protein and contains 4 water molecules and the sulphate anion. One of these solvent molecules is found at hydrogen bond distance from S70 and E166. S70 and S130 are hydrogen bonded to K73 and K234, respectively. It was found that the E. coli TEM1 and Staphylococcus aureus PC1 beta-lactamases crystal structures differ in the relative orientations of the two domains composing the enzymes, which result in a narrowed substrate binding cavity in the TEM1 enzyme. Local but significant differences in the vicinity of this site may explain the occurrence of TEM1 natural mutants with extended substrate specificities.
大肠杆菌TEM1β-内酰胺酶的X射线结构已针对5.0至1.8埃分辨率之间的22,510个反射进行了精修，结晶学R因子为16.4%；精修过程中纳入了199个水分子和1个硫酸根离子。除了少数暴露于溶剂中的侧链末端外，所有蛋白质原子都具有清晰的电子密度，精修后的平均原子温度因子为11埃²。估计的坐标误差为0.17埃。底物结合位点位于蛋白质两个结构域的界面处，包含4个水分子和硫酸根阴离子。其中一个溶剂分子与S70和E166的距离处于氢键距离。S70和S130分别与K73和K234形成氢键。研究发现，大肠杆菌TEM1和金黄色葡萄球菌PC1β-内酰胺酶的晶体结构在构成酶的两个结构域的相对取向上存在差异，这导致TEM1酶中的底物结合腔变窄。该位点附近局部但显著的差异可能解释了具有扩展底物特异性的TEM1天然突变体的出现。
