Conformation of sequential polypeptides of (Lysi‐Leuj), (Lysi‐Serj), and (Lys‐Gly) in sodium dodecyl sulfate solution
Conformation of sequential polypeptides of (Lysi‐Leuj), (Lysi‐Serj), and (Lys‐Gly) in sodium dodecyl sulfate solution
复制标题
(Lysi-Leuj)、(Lysi-Serj) 和 (Lys-Gly) 的连续多肽在十二烷基硫酸钠溶液中的构象
作者：
S. Kubota;K. Ikeda;Jen
合成了一系列序列多肽（LysiRj）n（R为Leu、Ser或Gly）和无规共聚肽（Lysx，Leuy）n。用圆二色谱法测定了它们在NaDodSO_4溶液中的构象。只有（Lys-Leu）n、（Lys-Ser）n和（Lys 3-Ser）n在表面活性剂溶液中采用稳定的β-形式;（Lys-Ser 2）n、（Lys-Ser 3）n、（Lys 2-Ser 2）n和（Lys 2-Ser）n具有不稳定的β-形式，其在高NaDodSO 4浓度下恢复为无序形式，即使Ser和DodSO 4−结合的Lys+都是β-形式。相比之下，（Lys-Gly）n在NaDodSO 4溶液中保持无序。另一方面，在NaDodSO 4溶液中，富含赖氨酸的（Lys 2-Leu）n形成不稳定的螺旋，而（Lys 2-Leu 2）n形成稳定的螺旋。在25 mM NaDodSO 4（Lysx，Leuy）中，n在x = 75时也形成螺旋，在x = 90时恢复为β-形式。这与（Lysx，Alay）n在x = 65时的螺旋构象和在x = 90时的β形式相比，表明Leu是比Ala更强的螺旋形成剂。我们的结果可能为NaDodSO 4溶液中许多蛋白质的螺旋度增加和β-形式的破坏提供了合理的解释，即蛋白质的多肽链在过量表面活性剂存在下通常有利于螺旋构象而不是β-形式。
A series of sequential polypeptides (LysiRj)n (R is Leu, Ser, or Gly) and random copolypeptides, (Lysx, Leuy)n, were synthesized. Their conformation in NaDodSO4 solution was determined by CD. Only (Lys‐Leu)n, (Lys‐Ser)n, and (Lys3‐Ser)n adopt a stable β‐form in the surfactant solution; (Lys‐Ser2)n, (Lys‐Ser3)n, (Lys2‐Ser2)n, and (Lys2‐Ser)n have an unstable β‐form, which reverts to an unordered form in high NaDodSO4 concentrations, even though both Ser and DodSO 4− ‐bound Lys+ are β‐formers. In contrast, (Lys‐Gly)n remains unordered in NaDodSO4 solution. On the other hand, Lys‐rich (Lys2‐Leu)n forms an unstable helix and (Lys2‐Leu2)n a stable helix in NaDodSO4 solution. In 25 mM NaDodSO4 (Lysx, Leuy)n also forms a helix up to x = 75 and reverts to the β‐form at x = 90. This compares with the helical conformation of (Lysx, Alay)n up to x = 65 and its β‐form at x = 90, suggesting that Leu is an even stronger helix‐former than Ala. Our results may provide a plausible explanation for the increase in helicity and disruption of the β‐form for many proteins in NaDodSO4 solution, that is, the polypeptide chain of a protein usually favors a helical conformation over a β‐form in the presence of excess surfactant.