Electrostatic contributions to T4 lysozyme stability: Solvent-exposed charges versus semi-buried salt bridges
Electrostatic contributions to T4 lysozyme stability: Solvent-exposed charges versus semi-buried salt bridges
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DOI：
10.1016/s0006-3495(02)73904-0
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发表时间：
2002-09-01
影响因子：
3.4
通讯作者：
Zhou, HX
中科院分区：
文献类型：
--
作者：
Dong, F;Zhou, HX
我们对五个暴露位点（K16E、R119E、K135E、K147E 和 R154E）的电荷反转以及 H31-D70 半埋盐桥的电荷中和和质子滴定对 T4 溶菌酶稳定性的影响进行了泊松-玻尔兹曼 (PB) 计算。我们没有使用广泛使用的溶剂排斥（SE）表面，而是使用范德华（vdW）表面作为蛋白质和溶剂电介质之间的边界（这是我们早期关于巴尔纳斯电荷突变的研究中建立的协议）。通过在未折叠状态下包含残余电荷-电荷相互作用，发现五个电荷反转突变的 DeltaDeltaG（未折叠）范围为 -1.6 至 1.3 kcal/mol。这表明马修斯和同事观察到的电荷反转的可变效应并不意外。发现 H31N、D70N 和 H31N/D70N 突变使蛋白质不稳定 2.9、1.3 和 1.6 kcal/mol，并且 H31 和 D70 的 pK(a) 值分别变为 9.4 和 0.6。这些结果与 Dahlquist 及其同事的实验数据非常吻合。相反，如果使用SE表面，H31N/D70N突变体将比野生型蛋白稳定1.3 kcal/mol。根据这些结果以及其他五种蛋白质的 27 个电荷突变的结果，我们得出结论：1）静电相互作用通常会不稳定的流行观点可能是基于由于使用 SE 表面作为介电边界而高估了去溶剂化成本； 2）虽然暴露于溶剂的电荷可能无法可靠地促进蛋白质稳定性，但半埋式盐桥可以提供显着的稳定性。
We carried our Poisson-Boltzmann (PB) calculations for the effects of charge reversal at five exposed sites (K16E, R119E, K135E, K147E, and R154E) and charge neutralization and proton titration of the H31-D70 semi-buried salt bridge on the stability of T4 lysozyme. Instead of the widely used solvent-exclusion (SE) surface, we used the van der Waals (vdW) surface as the boundary between the protein and solvent dielectrics (a protocol established in our earlier study on charge mutations in barnase). By including residual charge-charge interactions in the unfolded state, the five charge reversal mutations were found to have DeltaDeltaG(unfold) from -1.6 to 1.3 kcal/mol. This indicates that the variable effects of charge reversal observed by Matthews and co-workers are not unexpected. The H31N, D70N, and H31N/D70N mutations were found to destabilize the protein by 2.9, 1.3, and 1.6 kcal/mol, and the pK(a) values of H31 and D70 were shifted to 9.4 and 0.6, respectively. These results are in good accord with experimental data of Dahlquist and co-workers. In contrast, if the SE surface were used, the H31N/D70N mutant would be more stable than the wild-type protein by 1.3 kcal/mol. From these and additional results for 27 charge mutations on five other proteins, we conclude that 1) the popular view that electrostatic interactions are generally destabilizing may have been based on overestimated desolvation cost as a result of using the SE surface as the dielectric boundary; and 2) while solvent-exposed charges may not reliably contribute to protein stability, semi-buried salt bridges can provide significant stabilization.