Wimley W C, Gawrisch K, Creamer T P, White S H
Department of Physiology and Biophysics, University of California, Irvine 92717-4560, USA.
Proc Natl Acad Sci U S A. 1996 Apr 2;93(7):2985-90. doi: 10.1073/pnas.93.7.2985.
The solvation energies of salt bridges formed between the terminal carboxyl of the host pentapeptide AcWL- X-LL and the side chains of Arg or Lys in the guest (X) position have been measured. The energies were derived from octanol-to-buffer transfer free energies determined between pH 1 and pH 9. 13C NMR measurements show that the salt bridges form in the octanol phase, but not in the buffer phase, when the side chains and the terminal carboxyl group are charged. The free energy of salt-bridge formation in octanol is approximately -4 kcal/mol (1 cal = 4.184 J), which is equal to or slightly larger than the sum of the solvation energies of noninteracting pairs of charged side chains. This is about one-half the free energy that would result from replacing a charge pair in octanol with a pair of hydrophobic residues of moderate size. Therefore, salt bridging in octanol can change the favorable aqueous solvation energy of a pair of oppositely charged residues to neutral or slightly unfavorable but cannot provide the same free energy decrease as hydrophobic residues. This is consistent with recent computational and experimental studies of protein stability.
已测量了主体五肽AcWL-X-LL的末端羧基与客体（X）位置的Arg或Lys侧链之间形成的盐桥的溶剂化能。这些能量源自于在pH 1至pH 9之间测定的正辛醇-缓冲液转移自由能。13C NMR测量表明，当侧链和末端羧基带电时，盐桥在正辛醇相中形成，而不在缓冲相中形成。在正辛醇中形成盐桥的自由能约为-4 kcal/mol（1 cal = 4.184 J），这等于或略大于非相互作用带电侧链对的溶剂化能之和。这大约是用一对中等大小的疏水残基取代正辛醇中的电荷对所产生自由能的一半。因此，在正辛醇中形成盐桥可将一对带相反电荷残基的有利水溶剂化能变为中性或略为不利，但无法提供与疏水残基相同的自由能降低。这与最近关于蛋白质稳定性的计算和实验研究一致。
