Scholtz J M, Qian H, Robbins V H, Baldwin R L
Department of Biochemistry, Stanford University School of Medicine, California 94305-5307.
Biochemistry. 1993 Sep 21;32(37):9668-76. doi: 10.1021/bi00088a019.
A single pair of Glu and Lys residues has been placed at four different spacings, and in both orientations, in an otherwise neutral alanine-glutamine peptide helix, and the contribution to helix stability of the different Glu-Lys interactions has been measured. The contribution from the interaction of each charged side chain with the helix macrodipole has also been determined. A side-chain interaction between Gln and Glu, when the spacing is (i,i+4), has been detected and quantified. The interactions have been divided into contributions from hydrogen bonds (independent of the concentration of NaCl) and from electrostatic interactions (present in 10 mM NaCl, absent in 2.5 M NaCl). The major results are as follows: (1) The (i,i+3) and (i,i+4) Glu-Lys interactions are helix-stabilizing and are similar in strength to each other, regardless of the orientation of the side chains. (2) Hydrogen bonds provide the major contribution to these side-chain interactions, as shown by the following facts. First, the major part of the interaction observed in 10 mM NaCl, pH 7, is still present in 2.5 M NaCl. Second, the interaction found at pH 2 is equally as strong as that found in 2.5 M NaCl at pH 7. (3) The (i,i+4) Gln-Glu side-chain hydrogen bond is as strong as the hydrogen-bond component of the Glu-Lys interaction at both pH 2 and pH 7. The Gln-Glu interaction differs from the Glu-Lys interaction in being specific both for the orientation and the spacing of the residues. (4) No significant hydrogen-bonding interaction was found for the (i,i+1) or (i, i+2) Glu-Lys spacings, either at pH 2 or at pH 7, in 2.5 M NaCl. At 10 mM NaCl and pH 7, these spacings show a helix-destabilizing electrostatic interaction which probably results from stabilization of the coil conformation.
在一个原本中性的丙氨酸 - 谷氨酰胺肽螺旋中，一对谷氨酸（Glu）和赖氨酸（Lys）残基已被放置在四个不同的间距处，且两种方向都有，并且测量了不同Glu - Lys相互作用对螺旋稳定性的贡献。还确定了每个带电侧链与螺旋大偶极相互作用的贡献。当间距为（i，i + 4）时，已检测并量化了谷氨酰胺（Gln）和谷氨酸（Glu）之间的侧链相互作用。这些相互作用已被分为氢键贡献（与NaCl浓度无关）和静电相互作用贡献（存在于10 mM NaCl中，在2.5 M NaCl中不存在）。主要结果如下：（1）（i，i + 3）和（i，i + 4）的Glu - Lys相互作用可稳定螺旋，且强度彼此相似，与侧链的方向无关。（2）氢键对这些侧链相互作用起主要作用，如下事实所示。首先，在10 mM NaCl、pH 7时观察到的相互作用的主要部分在2.5 M NaCl中仍然存在。其次，在pH 2时发现的相互作用与在pH 7的2.5 M NaCl中发现的相互作用一样强。（3）在pH 2和pH 7时，（i，i + 4）的Gln - Glu侧链氢键与Glu - Lys相互作用的氢键成分一样强。Gln - Glu相互作用与Glu - Lys相互作用的不同之处在于，它对残基的方向和间距都具有特异性。（4）在2.5 M NaCl中，无论是在pH 2还是pH 7时，对于（i，i + 1）或（i，i + 2）的Glu - Lys间距，均未发现明显的氢键相互作用。在10 mM NaCl和pH 7时，这些间距显示出螺旋不稳定的静电相互作用，这可能是由于线圈构象的稳定化导致的。
