Jiang Dianlu, Dinh Kim Lien, Ruthenburg Travis C, Zhang Yi, Su Lei, Land Donald P, Zhou Feimeng
Department of Chemistry and Biochemistry, California State University, Los Angeles, Los Angeles, California 90032, USA.
J Phys Chem B. 2009 Mar 12;113(10):3160-8. doi: 10.1021/jp8085792.
At the air/buffer solution interface the kinetics of adsorption of amyloid beta peptide, Abeta(1-42), whose bulk concentration (submicromolar) is more than 2 orders of magnitude lower than that typically used in other in vitro aggregation studies, has been studied using a Langmuir-Blodgett trough. The pressure-time curves exhibit a lag phase, wherein the surface pressure essentially remains at zero, and a rising phase, corresponding to the Abeta adsorption at the interface. The duration of the lag phase was found to be highly dependent on both the Abeta bulk concentration and the solution temperature. A large activation energy (62.2 +/- 4.1 KJ/mol) was determined and the apparent adsorption rate constant was found to be linearly dependent on the Abeta bulk concentration. Attenuated total reflection-IR spectra of the adsorbed Abeta transferred to a solid substrate and circular dichroism measurements of Abeta in the solution layer near the interface reveal that the natively unstructured Abeta in the bulk undergo a conformation change (folding) to mainly the alpha-helical structure. The results suggest that, prior to the adsorption step, an equilibrium between Abeta conformations is established within the subsurface. The kinetic equation derived from this model confirms that the overall Abeta adsorption is kinetically controlled and the apparent rate constant is proportional to the Abeta bulk concentration. This model also indicates that interfaces such as cell membranes and lipid bilayers may facilitate Abeta aggregation/ fibrillation by providing a thin hydrophobic layer adjacent to the interface for the initial A/beta conformation change (misfolding) and accumulation. Such a preconcentration effect offers a plausible explanation of the fact that Abeta fibrillation occurs in vivo at nanomolar concentrations. Another important biological implication from our work is that Abeta misfolding may occur before its adsorption onto a cell membrane. This general kinetic model should also find applications in adsorption studies of other types of biomolecules whose overall kinetics exhibits a lag phase that is dependent on the bulk concentration of the adsorbate.
在空气/缓冲溶液界面，使用Langmuir-Blodgett槽研究了β淀粉样肽Abeta(1 - 42)的吸附动力学，其本体浓度（亚微摩尔）比其他体外聚集研究中通常使用的浓度低两个数量级以上。压力-时间曲线呈现一个滞后阶段，其中表面压力基本保持在零，以及一个上升阶段，对应于Abeta在界面处的吸附。发现滞后阶段的持续时间高度依赖于Abeta本体浓度和溶液温度。确定了较大的活化能（62.2±4.1 kJ/mol），并且发现表观吸附速率常数与Abeta本体浓度呈线性相关。转移到固体基质上的吸附Abeta的衰减全反射红外光谱以及界面附近溶液层中Abeta的圆二色性测量表明，本体中天然无结构的Abeta发生构象变化（折叠），主要转变为α-螺旋结构。结果表明，在吸附步骤之前，亚表面内Abeta构象之间建立了平衡。从该模型推导的动力学方程证实，总的Abeta吸附是动力学控制的，表观速率常数与Abeta本体浓度成正比。该模型还表明，诸如细胞膜和脂质双层等界面可能通过在界面附近提供一个薄的疏水层来促进Abeta聚集/纤维化，以实现初始A/beta构象变化（错误折叠）和积累。这种预浓缩效应为Abeta在体内以纳摩尔浓度发生纤维化这一事实提供了一个合理的解释。我们工作的另一个重要生物学意义是，Abeta错误折叠可能在其吸附到细胞膜上之前就发生了。这个通用的动力学模型也应该在其他类型生物分子的吸附研究中得到应用，这些生物分子的整体动力学表现出一个依赖于吸附质本体浓度的滞后阶段。
