Martinez Anna Victoria, Małolepsza Edyta, Domínguez Laura, Lu Qing, Straub John E
†Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States.
‡Division of Materials Science and Engineering, Boston University, 15 Saint Mary's Street, Brookline, Massachusetts 02446, United States.
J Phys Chem B. 2015 Jul 23;119(29):9084-90. doi: 10.1021/jp508813n. Epub 2014 Nov 6.
The propensity of peptides to form α-helices has been intensely studied using theory, computation, and experiment. Important model peptides for the study of the coil-to-helix transition have been alanine-lysine (AKA) peptides in which the lysine residues are placed on opposite sides of the helix avoiding charge repulsion while enhancing solubility. In this study, the effects of capped versus zwitterionic peptide termini on the secondary structure of alanine-rich peptides in reverse micelles are explored. The reverse micelles are found to undergo substantial shape fluctuations, a property observed in previous studies of AOT reverse micelles in the absence of solvated peptide. The peptides are observed to interact with water, as well as the AOT surfactant, including interactions between the nonpolar residues and the aliphatic surfactant tails. Computation of IR spectra for the amide I band of the peptide allows for direct comparison with experimental spectra. The results demonstrate that capped AKA2 peptides form more stable α helices than zwitterionic AKA2 peptides in reverse micelles. The rotational anisotropy decay of water is found to be distinctly different in the presence or absence of peptide within the reverse micelle, suggesting that the introduction of peptide significantly alters the number of free waters within the reverse micelle nanopool. However, neither the nature of the peptide termini (capped or charged) nor the degree of peptide helicity is found to significantly alter the balance of interactions between the peptides and the environment. Observed changes in the degree of helicity in AKA2 peptides in bulk solution and in reverse micelle environments result from changes in peptide confinement and hydration as well as direct nonpolar and polar interactions with the water-surfactant interface.
人们已运用理论、计算和实验等方法，深入研究了肽形成α螺旋的倾向。用于研究从卷曲到螺旋转变的重要模型肽是丙氨酸-赖氨酸（AKA）肽，其中赖氨酸残基位于螺旋的相对两侧，既能避免电荷排斥，又能提高溶解性。在本研究中，我们探究了封端肽与两性离子肽末端对反胶束中富含丙氨酸肽二级结构的影响。研究发现，反胶束会发生显著的形状波动，这一特性在先前关于无溶剂化肽的AOT反胶束研究中也有观察到。我们观察到肽与水以及AOT表面活性剂相互作用，包括非极性残基与脂肪族表面活性剂尾部之间的相互作用。通过计算肽的酰胺I带的红外光谱，可以直接与实验光谱进行比较。结果表明，在反胶束中，封端的AKA2肽比两性离子AKA2肽形成更稳定的α螺旋。研究发现，在反胶束中存在或不存在肽的情况下，水的旋转各向异性衰减明显不同，这表明肽的引入显著改变了反胶束纳米池中自由水的数量。然而，无论是肽末端的性质（封端或带电）还是肽的螺旋度，都未发现会显著改变肽与环境之间相互作用的平衡。在本体溶液和反胶束环境中观察到的AKA2肽螺旋度的变化，是由肽的受限程度和水合作用的变化以及与水-表面活性剂界面的直接非极性和极性相互作用导致的。
