Serrano L, Bycroft M, Fersht A R
Department of Chemistry, University of Cambridge, U.K.
J Mol Biol. 1991 Mar 20;218(2):465-75. doi: 10.1016/0022-2836(91)90725-l.
The side-chains of phenylalanine and tyrosine residues in proteins are frequently found to be involved in pairwise interactions. These occur both within repeating elements of secondary structure and in tertiary and quaternary interactions. It has been suggested that they are important in protein folding and stability, and non-bonded potential energy calculations indicate that a typical aromatic-aromatic interaction has an energy of between -1 and -2 kcal/mol and contributes between -0.6 and -1.3 kcal/mol to protein stability. There is such an aromatic pair on the solvent-exposed face of the first alpha-helix of barnase, the small ribonuclease from Bacillus amyloliquefaciens. The edge of the aromatic ring of Tyr17 interacts with the face of that of Tyr13. The two residues have been mutated both singly and pairwise to alanine, and their free energies of unfolding determined by denaturation with urea. Application of the double-mutant cycle analysis gives an interaction energy of -1.3 kcal/mol for the aromatic pair in the folded protein relative to solvation by water in the unfolded protein. This value is similar to that calculated from the change in surface-accessible area between the rings on the formation of the pair. Analysis of a further double-mutant cycle in which the Tyr residues are mutated to Phe indicates that the aromatic-aromatic interactions of Tyr/Tyr and Phe/Phe make identical contributions to protein stability. However, Tyr is preferred to Phe by 0.3(+/- 0.04) kcal/mol at the solvent-exposed face of the alpha-helix.
蛋白质中苯丙氨酸和酪氨酸残基的侧链经常参与成对相互作用。这些相互作用既发生在二级结构的重复元件中，也发生在三级和四级相互作用中。有人提出它们在蛋白质折叠和稳定性方面很重要，非键合势能计算表明，典型的芳香-芳香相互作用能量在-1至-2千卡/摩尔之间，对蛋白质稳定性的贡献在-0.6至-1.3千卡/摩尔之间。解淀粉芽孢杆菌的小核糖核酸酶巴那斯酶的第一个α-螺旋的溶剂暴露面上存在这样一对芳香族氨基酸。酪氨酸17的芳香环边缘与酪氨酸13的芳香环面相互作用。这两个残基已分别和成对突变为丙氨酸，并通过尿素变性测定它们的解折叠自由能。应用双突变循环分析得出，相对于未折叠蛋白质在水中的溶剂化，折叠蛋白质中芳香族氨基酸对的相互作用能量为-1.3千卡/摩尔。这个值与根据成对形成时环之间表面可及面积的变化计算得出的值相似。对酪氨酸残基突变为苯丙氨酸的另一个双突变循环的分析表明，酪氨酸/酪氨酸和苯丙氨酸/苯丙氨酸的芳香-芳香相互作用对蛋白质稳定性的贡献相同。然而，在α-螺旋的溶剂暴露面上，酪氨酸比苯丙氨酸更受青睐，相差0.3（±0.04）千卡/摩尔。
