Roychaudhuri Robin, Lomakin Aleksey, Bernstein Summer, Zheng Xueyun, Condron Margaret M, Benedek George B, Bowers Michael, Teplow David B
Department of Neurology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, CA 90095, USA.
Department of Physics and Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
J Mol Biol. 2014 Jun 26;426(13):2422-41. doi: 10.1016/j.jmb.2014.04.004. Epub 2014 Apr 13.
One of the earliest events in amyloid β-protein (Aβ) self-association is nucleation of Aβ monomer folding through formation of a turn at Gly25-Lys28. We report here the effects of structural changes at the center of the turn, Gly25-Ser26, on Aβ42 conformational dynamics and assembly. We used "click peptide" chemistry to quasi-synchronously create Aβ42 from 26-O-acyliso-Aβ42 (iAβ42) through a pH jump from 3 to 7.4. We also synthesized Nα-acetyl-Ser26-iAβ42 (Ac-iAβ42), which cannot undergo O→N acyl chemistry, to study the behavior of this ester form of Aβ42 itself at neutral pH. Data from experiments monitoring increases in β-sheet formation (thioflavin T, CD), hydrodynamic radius (RH), scattering intensity (quasielastic light scattering spectroscopy), and extent of oligomerization (ion mobility spectroscopy-mass spectrometry) were quite consistent. A rank order of Ac-iAβ42>iAβ42>Aβ42 was observed. Photochemically cross-linked iAβ42 displayed an oligomer distribution with a prominent dimer band that was not present with Aβ42. These dimers also were observed selectively in iAβ42 in ion mobility spectrometry experiments. The distinct biophysical behaviors of iAβ42 and Aβ42 appear to be due to the conversion of iAβ42 into "pure" Aβ42 monomer, a nascent form of Aβ42 that does not comprise the variety of oligomeric and aggregated states present in pre-existent Aβ42. These results emphasize the importance of the Gly25-Ser26 dipeptide in organizing Aβ42 monomer structure and thus suggest that drugs altering the interactions of this dipeptide with neighboring side-chain atoms or with the peptide backbone could be useful in therapeutic strategies targeting formation of Aβ oligomers and higher-order assemblies.
淀粉样β蛋白（Aβ）自组装过程中最早发生的事件之一是Aβ单体通过在Gly25-Lys28处形成一个转角进行折叠成核。我们在此报告转角中心Gly25-Ser26处的结构变化对Aβ42构象动力学和组装的影响。我们使用“点击肽”化学方法，通过将pH从3跃升至7.4，从26-O-酰基异Aβ42（iAβ42）准同步生成Aβ42。我们还合成了不能进行O→N酰基化学反应的Nα-乙酰基-Ser26-iAβ42（Ac-iAβ42），以研究这种Aβ42酯形式在中性pH下自身的行为。监测β-折叠形成增加（硫黄素T、圆二色光谱）、流体动力学半径（RH）、散射强度（准弹性光散射光谱）和寡聚化程度（离子淌度光谱-质谱）的实验数据相当一致。观察到Ac-iAβ42>iAβ42>Aβ42的排序。光化学交联的iAβ42显示出一种寡聚体分布，其中有一个突出的二聚体条带，而Aβ42则没有。在离子淌度光谱实验中，也在iAβ42中选择性地观察到了这些二聚体。iAβ42和Aβ42不同的生物物理行为似乎是由于iAβ42转化为“纯”Aβ42单体，这是一种新生的Aβ42形式，不包含预先存在的Aβ42中存在的各种寡聚和聚集状态。这些结果强调了Gly25-Ser26二肽在组织Aβ42单体结构中的重要性，因此表明改变该二肽与相邻侧链原子或肽主链相互作用的药物可能在针对Aβ寡聚体和高阶组装形成的治疗策略中有用。
