Characterization of the enzymatic properties of γ-secretase

长期以来，细胞膜内的分裂是如何进行的一直是个谜。我们之前假设βCTF首先在膜-细胞质边界被切割，产生两个长Ass， Aβ48和Aβ49，它们在每一步释放三个残基，分别被加工成Aβ42和Aβ40。为了验证这一假设，我们使用LC-MS/MS来量化假设释放的特定三肽。利用chapso重组的γ-分泌酶系统，我们证实了Aβ49通过连续释放2或3个三肽转化为Aβ43/40， Aβ48通过连续释放2个三肽或这些三肽加一个额外的四肽转化为Aβ42/38。

How the cleavage proceeds within the membrane has long been enigmatic. We previously hypothesized that βCTF is cleaved first at the membrane-cytoplasm boundary, producing two long Ass, Aβ48 and Aβ49, which are processed further by releasing three residues at each step to produce Aβ42 and Aβ40, respectively. To test this hypothesis, we used LC-MS/MS to quantify the specific tripeptides that are postulated to be released. Using CHAPSO-reconstituted γ-secretase system, we confirmed that Aβ49 is converted to Aβ43/40 by successively releasing two or three tripeptides, and that Aβ48 is converted to Aβ42/38 by successively releasing two tripeptides or these plus an additional tetrapeptide.