Department of Neuropathology, Graduate School of Life and Medical Sciences, Doshisha University, Kyoto, Japan.
Neuropsychiatry, Department of Integrated Medicine, Division of Internal Medicine, Osaka University Graduate School of Medicine, Suita, Japan.
Semin Cell Dev Biol. 2020 Sep;105:64-74. doi: 10.1016/j.semcdb.2020.04.002. Epub 2020 Apr 27.
γ-Secretase is a multimeric aspartyl protease that cleaves the membrane-spanning region of the β-carboxyl terminal fragment (βCTF) generated from β-amyloid precursor protein. γ-Secretase defines the generated molecular species of amyloid β-protein (Aβ), a critical molecule in the pathogenesis of Alzheimer's disease (AD). Many therapeutic trials for AD have targeted γ-secretase. However, in contrast to the great efforts in drug discovery, the enzymatic features and cleavage mechanism of γ-secretase are poorly understood. Here we review our protein-chemical analyses of the cleavage products generated from βCTF by γ-secretase, which revealed that Aβ was produced by γ-secretase through successive cleavages of βCTF, mainly at three-residue intervals. Two representative product lines were identified. ε-Cleavages occur first at Leu49-Val50 and Thr48-Leu49 of βCTF (in accordance with Aβ numbering). Longer generated Aβs, Aβ49 and Aβ48, are precursors to the majority of Aβ40 and Aβ42, concomitantly releasing the tripeptides, ITL, VIV, and IAT; and VIT and TVI, respectively. A portion of Aβ42 is processed further to Aβ38, releasing a tetrapeptide, VVIA. The presence of additional multiple minor pathways may reflect labile cleavage activities derived from the conformational flexibility of γ-secretase through molecular interactions. Because these peptide byproducts are not secreted and remain within the cells, they may serve as an indicator that reflects γ-secretase activity more directly than secreted Aβ.
γ-分泌酶是一种多聚天冬氨酸蛋白酶，可切割β-淀粉样前体蛋白（APP）产生的跨膜区β-羧基末端片段（βCTF）。γ-分泌酶定义了淀粉样β-蛋白（Aβ）的产生分子种类，Aβ是阿尔茨海默病（AD）发病机制中的关键分子。许多 AD 的治疗试验都针对 γ-分泌酶。然而，与药物发现的巨大努力相比，γ-分泌酶的酶学特征和切割机制还了解甚少。在这里，我们回顾了我们对 γ-分泌酶切割βCTF 产生的切割产物的蛋白质化学分析，这些分析表明，Aβ是通过 γ-分泌酶对βCTF 的连续切割产生的，主要是在三个残基间隔处。鉴定出两条有代表性的产物线。ε-切割首先发生在βCTF 的 Leu49-Val50 和 Thr48-Leu49 处（与 Aβ 编号一致）。生成的较长 Aβs，Aβ49 和 Aβ48，是大多数 Aβ40 和 Aβ42 的前体，同时释放三肽 ITL、VIV 和 IAT；以及 VIT 和 TVI，分别。一部分 Aβ42 进一步加工为 Aβ38，释放四肽 VVIA。存在额外的多条次要途径可能反映了 γ-分泌酶通过分子相互作用产生的构象灵活性导致的不稳定切割活性。由于这些肽类副产物不分泌并保留在细胞内，它们可能作为指标，比分泌的 Aβ更直接地反映 γ-分泌酶活性。
