HELIX STABILIZATION BY GLU- ... LYS+ SALT BRIDGES IN SHORT PEPTIDES OF DENOVO DESIGN
HELIX STABILIZATION BY GLU- ... LYS+ SALT BRIDGES IN SHORT PEPTIDES OF DENOVO DESIGN
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DOI：
10.1073/pnas.84.24.8898
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发表时间：
1987-12-01
影响因子：
11.1
通讯作者：
BALDWIN, RL
中科院分区：
文献类型：
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作者：
MARQUSEE, S;BALDWIN, RL
设计、合成了四种基于丙氨酸的肽，并通过圆二色性检测它们在水中形成α - 螺旋的情况。每种肽都有三对谷氨酸/赖氨酸残基，长度为16或17个氨基酸，并且α - NH₂和α - COOH基团被封闭。在一组肽（“i + 4”）中，谷氨酸和赖氨酸残基相隔4个残基或1个残基。在另一组（“i + 3”）中，间隔为3个或2个残基。在每组肽中，制备了一对肽，其中谷氨酸和赖氨酸残基的位置是相反的[谷氨酸，赖氨酸（E，K）与赖氨酸，谷氨酸（K，E）]，以评估带电侧链与螺旋偶极的相互作用。由于这些肽的氨基酸组成最多只有一个丙氨酸残基的差异，螺旋度的差异主要是由带电残基的间隔和位置引起的。本研究的基本目的是测试（谷氨酸⁻，赖氨酸⁺）离子对或盐桥（氢键连接的离子对）对螺旋的稳定作用。结果如下：
（i）所有四种肽都显示出明显的螺旋形成，并且在研究的范围内，α - 螺旋的稳定性不依赖于肽的浓度。最佳的螺旋形成肽是（i + 4）E，K，它在pH 7、0℃、0.01 M NaCl中显示出约80%的螺旋度。
（ii）两种i + 4肽比i + 3肽显示出更多的螺旋形成，pH滴定没有证据表明i + 3离子对能稳定螺旋。
（iii）令人惊讶的是，在极端pH（pH 2和pH 12）以及pH 7时，i + 4肽比i + 3肽形成更稳定的螺旋。这些结果可以通过在pH 7时通过谷氨酸⁻···赖氨酸⁺盐桥以及在pH 2（谷氨酸⁰···赖氨酸⁺）和pH 12（谷氨酸⁻···赖氨酸⁰）时通过单电荷氢键来稳定螺旋来解释。为什么这些连接在i + 4肽中比在i + 3肽中更有效地稳定α - 螺旋的原因尚不清楚。
（iv）谷氨酸和赖氨酸残基位置的颠倒通常以这些带电基团与螺旋偶极相互作用所预期的方式影响螺旋稳定性。
（v）在这些基于丙氨酸的肽中，α - 螺旋的形成是由焓驱动的，就像核糖核酸酶A的C - 肽形成螺旋一样。
Four alanine-based peptides were designed, synthesized, and tested by circular dichroism for .alpha.-helix formation in H2O. Each peptide has three glutamic/lysine residue pairs, is 16 or 17 amino acids long, and has blocked .alpha.-NH2 and .alpha.-COOH groups. In one set of peptides ("i + 4"), the glutamic and lysine residues are spaced 4 residues or 1 residue apart. In the other set ("i + 3"), the spacing is 3 or 2 residues. Within each of these sets, a pair of peptides was made in which the positions of the glutamic and lysine residues are reversed [Glu, Lys (E,K) vs. Lys, Glu (K,E)] in order to assess the interaction of the charged side chains with the helix dipole. Since the amino acid compositions of these peptides differ at most by a single alanine residue, differences in helicity are caused chiefly by the spacing and positions of the charged residues. The basic aim of this study was to test for helix stabilization by (Glu-, Lys+) ion pairs or salt bridges (H-bonded ion pairs). The results are as follows. (i) All four peptides show significant helix formation, and the stability of the .alpha.-helix does not depend on peptide concentration in the range studied. The best helix-former is (i + 4)E,K, which shows .apprxeq. 80% helicity in 0.01 M NaCl at pH 7 and 0.degree. C. (ii) The two i + 4 peptides show more helix formation than the i + 3 peptides pH titration gives no evidence for helix stabilization by i + 3 ion pairs. (iii) Surprisingly, the i + 4 peptides form more stable helices than the i + 3 peptides at extremes of pH (pH 2 and pH 12) as well as at pH 7. These results may be explained by helix stabilization through Glu- .tplbond. Lys+ salt bridges at pH 7 and singly charged H bonds at pH 2 (Glu0 .tplbond. Lys+) and pH 12 (Glu- .tplbond. Lys0). The reason why these links stabilize the .alpha.-helix more effectively in the i + 4 than in the i + 3 peptides is not known. (iv) Reversal of the positions of glutamic and lysine residues usually affects helix stability in the manner expected for interaction of these charged groups with the helix dipole. (v) .alpha.-Helix formation in these alanine-based peptides is enthalpy-driven, as is helix formation by the C-peptide of ribonuclease A.