Caballero Leonardo, Mena Juan, Morales-Alvarez Aurora, Kogan Marcelo J, Melo Francisco
Departamento de Física, Universidad de Santiago , Avenida Ecuador 3493, Casilla 307, Correo 2, Santiago, Chile.
Langmuir. 2015;31(1):299-306. doi: 10.1021/la502777h. Epub 2014 Dec 22.
We present a method based on atomic force microscopy (AFM) to assess the work of adhesion between the interfaces of gold AFM tips functionalized with three peptides derived from β-sheet breaker LPFFD [CLPFFD-NH2 (i0) and their isomers CDLPFF-NH2 (i1) and CLPDFF-NH2 (i2)], and the beta-amyloid protein (Aβ1-42). β-Amyloid protein was deposited onto a highly oriented graphite (HOPG) surface as protofibrils and fibrils. The presence of the residues Leu (L), Phe (F), and Phe (F), which are also present in the native sequence, confirm that the peptides are able to bind to the aggregates of Aβ1-42 fibrils and protofibrils. Force of adhesion data were directly obtained from the maximum force on retraction, and the work of adhesion was calculated from the Jhonson-Kendall-Roberts model (JKR-Model). Both the polar and dispersive contributions to the surface energy of the peptides i0, i1, and i2, as well as Aβ1-42 fibrils and protofibrils, were determined by means of measuring the contact angle and using the two-fluid method. The macroscopic energies of the functionalized gold surfaces do not differ significantly between isomers, which confirms the similar nature of the peptides i0, i1, and i2 but suggests that the macroscopic measurements are not able to distinguish specific sequences. The nanoprobe reveals a typical adhesion work value associated with the interaction of protofibrils with i0 and i2; this value is three times higher than that of i1. The difference is attributed to the hydrophobic nature of protofibrils, the predominant exposition of hydrophobic residues of the peptides i0 and i2, with respect to i1, and the degree of functionalization. i0 and i2 presented a slight adhesion with Aβ fibrils, which is associated with the exposed hydrophilic groups of these fibrils (onto HOPG) compared to the protofibrils. However, i1 showed interaction with both Aβ fibrils and protofibrils. For this, we propose an explanation based on the fact that the peptide i1 locates itself adjacent to the gold surface of the probe, concealing their hydrophobic groups and therefore decreasing the probability of interaction with Aβ fibrils and protofibrils. The peptide-gold nano probe represents a useful tool to study the nanobiointeractions of functionalized nanoparticles with amyloid aggregates.
我们提出了一种基于原子力显微镜（AFM）的方法，用于评估用源自β-折叠破坏肽LPFFD的三种肽[CLPFFD-NH2（i0）及其异构体CDLPFF-NH2（i1）和CLPDFF-NH2（i2）]功能化的金AFM探针界面与β-淀粉样蛋白（Aβ1-42）之间的粘附功。β-淀粉样蛋白以原纤维和纤维形式沉积在高度取向的石墨（HOPG）表面上。天然序列中也存在的亮氨酸（L）、苯丙氨酸（F）和苯丙氨酸（F）残基的存在，证实了这些肽能够与Aβ1-42纤维和原纤维的聚集体结合。粘附力数据直接从回缩时的最大力获得，粘附功根据约翰逊-肯德尔-罗伯茨模型（JKR模型）计算。通过测量接触角并使用双流体法，确定了肽i0、i1和i2以及Aβ1-42纤维和原纤维表面能的极性和色散贡献。功能化金表面的宏观能量在异构体之间没有显著差异，这证实了肽i0、i1和i2的相似性质，但表明宏观测量无法区分特定序列。纳米探针揭示了与原纤维与i0和i2相互作用相关的典型粘附功值；该值比i1高两倍。这种差异归因于原纤维的疏水性、肽i0和i2相对于i1的疏水残基的主要暴露以及功能化程度。i0和i2与Aβ纤维有轻微粘附，这与这些纤维（在HOPG上）与原纤维相比暴露的亲水基团有关。然而，i1显示出与Aβ纤维和原纤维都有相互作用。为此，我们基于肽i1位于探针金表面附近这一事实提出一种解释，隐藏了它们的疏水基团，因此降低了与Aβ纤维和原纤维相互作用的可能性。肽-金纳米探针是研究功能化纳米颗粒与淀粉样聚集体的纳米生物相互作用的有用工具。
