Worthylake D, Meadow N D, Roseman S, Liao D I, Herzberg O, Remington S J
Department of Physics, University of Oregon, Eugene 97403.
Proc Natl Acad Sci U S A. 1991 Dec 1;88(23):10382-6. doi: 10.1073/pnas.88.23.10382.
The crystal structure of a proteolytically modified form of the Escherichia coli phosphocarrier and signal transducing protein IIIglc has been determined by multiple isomorphous and molecular replacement. The model has been refined to an R-factor of 0.166 for data between 6- and 2.1-A resolution with an rms deviation of 0.020 A from ideal bond lengths and 3.2 degrees from ideal bond angles. The molecule is a beta-sheet sandwich, with six antiparallel strands on either side. Several short distorted helices line the periphery of the active site, which is a shallow extremely hydrophobic depression approximately 18 A in diameter near the center of one face. The side chains of the active site histidine residues 75 and 90 face each other at the center of the depression, with the N3 positions exposed to solvent, separated by 3.3 A in an excellent position to form adducts with phosphate. Chloroplatinate forms a divalent adduct with both histidyl side chains, suggesting that the phosphodonor reaction might proceed through a similar transition state. The hydrophobic patch forms the primary crystal contact, suggesting a mode of association of IIIglc with other components of the phosphoenolpyruvate-dependent phosphotransferase system.
通过多重同晶置换和分子置换法，已确定了经蛋白水解修饰的大肠杆菌磷酸载体及信号转导蛋白IIIglc的晶体结构。对于分辨率在6至2.1埃之间的数据，该模型已精修至R因子为0.166，与理想键长的均方根偏差为0.020埃，与理想键角的偏差为3.2度。该分子为β-折叠三明治结构，两侧各有六条反平行链。活性位点周围排列着几条短的扭曲螺旋，活性位点是一个浅的极疏水凹陷，位于一个面中心附近，直径约18埃。活性位点组氨酸残基75和90的侧链在凹陷中心彼此相对，N3位置暴露于溶剂中，相距3.3埃，处于与磷酸盐形成加合物的极佳位置。氯铂酸盐与两个组氨酸侧链形成二价加合物，表明磷酸供体反应可能通过类似的过渡态进行。疏水区域形成主要的晶体接触，提示了IIIglc与磷酸烯醇丙酮酸依赖性磷酸转移酶系统其他组分的缔合模式。
