Investigating the Effect of pH on the Aggregation of Two Surfactant-Like Octapeptides
Investigating the Effect of pH on the Aggregation of Two Surfactant-Like Octapeptides
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DOI：
10.1021/la904528p
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发表时间：
2010-04-20
期刊：
影响因子：
3.9
通讯作者：
Windle, Alan H.
中科院分区：
文献类型：
--
作者：
Capes, Jacqueline S.;Kiley, Patrick J.;Windle, Alan H.
用滴定法、圆二色谱法（CD）和傅里叶变换红外光谱法（FTIR）研究了两种新设计的表面活性剂样肽（Ac-IIKKEENN-OH（Pt）和Ac-IIEENNOD-OH（P2））在不同pH值水溶液中的聚集行为。和原子力显微镜（AFM）。发现P_1和P_2的聚集体均显示5 pK（a）。其中一些与那些氨基酸的表列值有相当大的不同。特别地，P1的赖氨酸滴定至4.939 +/-0.066。P1的CD光谱对pH不敏感，而P2的CD光谱显示随着pH降低，无规卷曲到β-折叠转变。AFM图像证实P1聚集体在所有pH值下均为球形，大小范围为3 - 20 nm。另一方面，P2聚集体在低于pH 4时为扭曲的带状，但在高于pH 4时为小于10 nm的球形。此外，AFM图像表明，这些扭曲的带状物的部分破裂后，升高的pH值从3.03到3.46和带状物在pH值3.82的虚拟消失。P2的FTIR光谱表明，随着pH的降低，从无规卷曲到β-折叠的结构转变。骨架氢键以及电荷的作用进行了讨论。
The aggregation of two de novo designed surfactant-like peptides, with sequences Ac-IIKKEENN OH (Pt) and Ac-IIEENNOD-OH (P2), has been studied in aqueous solution at various pH values using titration, Circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR). and atomic force microscopy (AFM). It was found that aggregates of P1 and P2 both display 5 pK(a)'s. some of which differ considerably from the tabulated values for those amino acids. In particular, a lysine of P1 titrated to 4.939 +/- 0.066. CD spectra of P1 were insensitive to pH, while CD spectra of P2 demonstrated a random coil-to-beta-sheet transition as pH was decreased. AFM images confirmed that P1 aggregates were spheres at all pH values and ranged in size from 3 to 20 nm. On the other hand, P2 aggregates were twisted ribbons below pH 4 but spheres less than 10 nm above pH 4. In addition, AFM images demonstrated the partial breakup of these twisted ribbons upon elevating the pH from 3.03 to 3.46 and the virtual disappearance of ribbons at pH 3.82. FTIR spectra of P2 indicate a structural transition from random coil to beta-sheet as pH was decreased. The role of backbone hydrogen bonding as well as charge is discussed.