Somatostatin, an <i>In Vivo</i> Binder to Aβ Oligomers, Binds to βPFO_Aβ(1–42) Tetramers

Somatostatin (SST14) is strongly related to Alzheimer’s disease (AD), as its levels decline during aging, it regulates the proteolytic degradation of the amyloid beta peptide (Aβ), and it binds to Aβ oligomers in vivo. Recently, the 3D structure of a membrane-associated β-sheet pore-forming tetramer (βPFOAβ(1–42) tetramer) has been reported. Here, we show that SST14 binds selectively to the βPFOAβ(1–42) tetramer with a KD value of ∼40 μM without binding to monomeric Aβ(1–42). Specific NMR chemical shift perturbations, observed during titration of SST14, define a binding site in the βPFOAβ(1–42) tetramer and are in agreement with a 2:1 stoichiometry determined by both native mass spectroscopy and isothermal titration calorimetry. These results enabled us to perform driven docking and model the binding mode for the interaction. The present study provides additional evidence on the relation between SST14 and the amyloid cascade and positions the βPFOAβ(1–42) tetramer as a relevant aggregation form of Aβ and as a potential target for AD.生长抑素（Somatostatin, SST14）与阿尔茨海默病（Alzheimer’s disease, AD）密切相关：其水平随衰老进程下降，可调控淀粉样β肽（Amyloid beta peptide, Aβ）的蛋白水解降解，并可在体内与Aβ寡聚体结合。近期，有研究报道了一种膜结合型β折叠成孔四聚体（βPFOAβ(1–42) tetramer）的三维结构。本研究发现，SST14可选择性结合βPFOAβ(1–42)四聚体，解离常数（KD）约为40 μM，而不与单体Aβ(1–42)结合。在SST14滴定实验中观测到的特异性核磁共振（Nuclear Magnetic Resonance, NMR）化学位移扰动，明确了βPFOAβ(1–42)四聚体上的结合位点，且该结果与通过天然质谱（native mass spectroscopy）和等温滴定量热法（isothermal titration calorimetry）所确定的2:1化学计量比相符。基于上述结果，我们开展了定向对接实验，并构建了该相互作用的结合模式模型。本研究为SST14与淀粉样蛋白级联反应之间的关联提供了额外佐证，并确立了βPFOAβ(1–42)四聚体作为Aβ的关键聚集形式以及阿尔茨海默病潜在治疗靶点的地位。