Ledvina P S, Yao N, Choudhary A, Quiocho F A
Howard Hughes Medical Institute and Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 1996 Jun 25;93(13):6786-91. doi: 10.1073/pnas.93.13.6786.
Determination of the crystal structure of an "open" unliganded active mutant (T141D) form of the Escherichia coli phosphate receptor for active transport has allowed calculation of the electrostatic surface potential for it and two other comparably modeled receptor structures (wild type and D137N). A discovery of considerable implication is the intensely negative potential of the phosphate-binding cleft. We report similar findings for a sulfate transport receptor, a DNA-binding protein, and, even more dramatically, redox proteins. Evidently, for proteins such as these, which rely almost exclusively on hydrogen bonding for anion interactions and electrostatic balance, a noncomplementary surface potential is not a barrier to binding. Moreover, experimental results show that the exquisite specificity and high affinity of the phosphate and sulfate receptors for unions are insensitive to modulations of charge potential, but extremely sensitive to conditions that leave a hydrogen bond donor or acceptor unpaired.
对大肠杆菌用于主动运输的磷酸盐受体的一种“开放”的未结合配体的活性突变体（T141D）形式的晶体结构进行测定，使得能够计算出该结构以及其他两种类似建模的受体结构（野生型和D137N）的静电表面电势。一个具有重大意义的发现是磷酸盐结合裂隙处强烈的负电势。我们报道了硫酸盐转运受体、一种DNA结合蛋白，甚至更显著地，氧化还原蛋白也有类似的发现。显然，对于这些几乎完全依赖氢键进行阴离子相互作用和静电平衡的蛋白质来说，非互补的表面电势并不是结合的障碍。此外，实验结果表明，磷酸盐和硫酸盐受体对结合物的精确特异性和高亲和力对电荷电势的调节不敏感，但对使氢键供体或受体未配对的条件极其敏感。
