Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison53706, Wisconsin, United States.
Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison53706, Wisconsin, United States.
Langmuir. 2021 Mar 23;37(11):3288-3298. doi: 10.1021/acs.langmuir.0c03255. Epub 2021 Mar 8.
Hydrophobic interactions mediated by nonpolar molecular fragments in water are influenced by local chemical and physical contexts in ways that are not yet fully understood. Here, we use globally amphiphilic (GA) β-peptides (GA-Lys and GA-Arg) with stable conformations to explore if replacement of β-homolysine (βLys) with β-homoarginine (βArg) influences the hydrophobically driven assembly of these peptides in bulk aqueous solution. The studies were conducted in 10 mM triethanolamine buffer at pH 7, where both βLys (ammonium) and βArg (guanidinium) side chains are substantially protonated. Comparisons of light scattering measurements and cryo-electron micrographs before and after the addition of 60 vol% MeOH indicate very different outcomes of the hydrophobically driven assembly of AcY-GA-Lys versus AcY-GA-Arg (AcY denotes an N-acetylated-β-homotyrosine (βTyr) at each N-terminus). Nuclear magnetic resonance and analytical ultracentrifugation confirm that AcY-GA-Lys assembles into large aggregates in aqueous buffer, whereas AcY-GA-Arg at comparable concentrations forms only small oligomers. Titration of AcY-GA-Arg into aqueous solutions of AcY-GA-Lys reveals that the driving force for AcY-GA-Lys association is far stronger than that for AcY-GA-Arg association. We discuss these results in the light of past experimental observations involving single molecule force measurements with GA β-peptides and hydrophobically driven dimerization of conventional peptides that form a GA α-helix upon dimerization (but do not display the Lys versus Arg trend predicted by extrapolating from the earlier AFM studies with β-peptides). Overall, our results establish that the identity of proximal cationic groups, ammonium versus guanidinium, profoundly modulates the hydrophobically driven self-assembly of conformationally stable β-peptides in bulk aqueous solution.
在水中，非极性分子片段通过疏水相互作用介导，其方式受到局部化学和物理环境的影响，但尚未完全理解。在这里，我们使用具有稳定构象的全局两亲性 (GA) β-肽 (GA-Lys 和 GA-Arg) 来探索β-同赖氨酸 (βLys) 被β-同精氨酸 (βArg) 取代是否会影响这些肽在大体积水溶液中的疏水性驱动组装。研究在 pH 7 的 10 mM 三乙醇胺缓冲液中进行，其中βLys（铵）和βArg（胍基）侧链都大量质子化。在添加 60 体积%甲醇前后进行光散射测量和低温电子显微镜比较表明，AcY-GA-Lys 和 AcY-GA-Arg（AcY 表示每个 N 端的 N-乙酰基-β-同酪氨酸 (βTyr)）的疏水性驱动组装的结果非常不同。核磁共振和分析超速离心证实，AcY-GA-Lys 在水溶液缓冲液中组装成大聚集体，而在可比浓度下的 AcY-GA-Arg 仅形成小寡聚物。将 AcY-GA-Arg 滴定到 AcY-GA-Lys 的水溶液中表明，AcY-GA-Lys 缔合的驱动力远强于 AcY-GA-Arg 缔合的驱动力。我们根据过去涉及 GA β-肽的单分子力测量的实验观察结果以及在二聚化时形成 GA α-螺旋的常规肽的疏水性驱动二聚化（但不显示通过从早期与β-肽的 AFM 研究外推预测的 Lys 与 Arg 趋势）来讨论这些结果。总的来说，我们的结果表明，临近阳离子基团的身份，铵与胍基，深刻地调节了构象稳定的β-肽在大体积水溶液中的疏水性驱动自组装。
