Adolf-Butenandt-Institute, Biochemistry, Ludwig-Maximilians-University, 80336 Munich, Germany.
J Biol Chem. 2011 Oct 28;286(43):37181-6. doi: 10.1074/jbc.C111.276972. Epub 2011 Sep 6.
γ-Secretase is essential for the generation of the neurotoxic 42-amino acid amyloid β-peptide (Aβ(42)). The aggregation-prone hydrophobic peptide, which is deposited in Alzheimer disease (AD) patient brain, is generated from a C-terminal fragment of the β-amyloid precursor protein by an intramembrane cleavage of γ-secretase. Because Aβ(42) is widely believed to trigger AD pathogenesis, γ-secretase is a key AD drug target. Unlike inhibitors of the enzyme, γ-secretase modulators (GSMs) selectively lower Aβ(42) without interfering with the physiological function of γ-secretase. The molecular target(s) of GSMs and hence the mechanism of GSM action are not established. Here we demonstrate by using a biotinylated photocross-linkable derivative of highly potent novel second generation GSMs that γ-secretase is a direct target of GSMs. The GSM photoprobe specifically bound to the N-terminal fragment of presenilin, the catalytic subunit of γ-secretase, but not to other γ-secretase subunits. Binding was differentially competed by GSMs of diverse structural classes, indicating the existence of overlapping/multiple GSM binding sites or allosteric alteration of the photoprobe binding site. The β-amyloid precursor protein C-terminal fragment previously implicated as the GSM binding site was not targeted by the compound. The identification of presenilin as the molecular target of GSMs directly establishes allosteric modulation of enzyme activity as a mechanism of GSM action and may contribute to the development of therapeutically active GSMs for the treatment of AD.
γ-分泌酶对于神经毒性的 42 个氨基酸淀粉样β肽（Aβ（42））的产生至关重要。这种易于聚集的疏水性肽在阿尔茨海默病（AD）患者的大脑中沉积，是由β淀粉样前体蛋白的 C 端片段通过γ-分泌酶的跨膜切割产生的。由于广泛认为 Aβ（42）触发 AD 发病机制，γ-分泌酶是 AD 的关键药物靶点。与酶抑制剂不同，γ-分泌酶调节剂（GSMs）选择性地降低 Aβ（42）而不干扰γ-分泌酶的生理功能。GSM 的分子靶标（s）及其作用机制尚未建立。在这里，我们通过使用高度有效的新型第二代 GSM 的生物素化光交联衍生剂证明了 γ-分泌酶是 GSM 的直接靶标。GSM 光探针特异性结合到 γ-分泌酶的催化亚基早老素的 N 端片段，但不与其他 γ-分泌酶亚基结合。不同结构类别 GSM 的竞争结合表明存在重叠/多个 GSM 结合位点或变构改变光探针结合位点。先前被认为是 GSM 结合位点的β淀粉样前体蛋白 C 端片段未被该化合物靶向。将早老素鉴定为 GSM 的分子靶标直接确定了酶活性的变构调节是 GSM 作用的机制，并可能有助于开发治疗 AD 的具有治疗活性的 GSM。
