Alzheimer Presenilin-1 Mutations Dramatically Reduce Trimming of Long Amyloid β-Peptides (Aβ) by γ-Secretase to Increase 42-to-40-Residue Aβ
Alzheimer Presenilin-1 Mutations Dramatically Reduce Trimming of Long Amyloid β-Peptides (Aβ) by γ-Secretase to Increase 42-to-40-Residue Aβ
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DOI：
10.1074/jbc.m114.581165
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发表时间：
2014-11-07
影响因子：
4.8
通讯作者：
Wolfe, Michael S.
中科院分区：
文献类型：
--
作者：
Fernandez, Marty A.;Klutkowski, Julia A.;Wolfe, Michael S.
含有早老素的γ-分泌酶复合物通过膜内蛋白水解产生淀粉样β-肽（A β），并且>100个早老素突变与家族性早发性阿尔茨海默病（AD）相关。这些突变是否通过功能的获得或丧失导致AD的问题仍然存在很大争议。早老素的突变增加了发病关键的42- 40-残基A β的比例，但其他38 - 49残基的A β也由γ-分泌酶形成。细胞中的证据表明，蛋白酶首先在E位点处切割跨膜结构域内的底物，以形成48或49个残基的A β。从C末端开始，几乎每隔三个残基就发生一次裂解，这被认为是沿着沿着两条途径向较短的A β分泌形式发生的：A β 49 -> A β 46 -> A β 43 -> A β 40和A β 48 -> A β 45 -> A β 42 -> A β 38。在这里，我们表明，添加合成的长A β肽（A β 45- 49）直接到纯化的γ-分泌酶制剂导致A β 40和A β 42的形成，无论蛋白酶复合物是洗涤剂溶解或重组到脂质囊泡中，和产品A β 42的比例A β 40遵循的模式与双途径假说一致。对早老素-1的五种不同的AD致突变的动力学分析表明，所有突变都导致正常羧肽酶功能的急剧降低。突变蛋白酶对长A β肽至A β 40和A β 42的修饰改变发生在多个水平上，与E位点对初始内蛋白水解的影响无关，所有这些共同增加了与A β发病机制有关的关键A β 42/A β 40比率。总之，这些结果表明，γ-分泌酶的羧肽酶功能的特异性降低导致毒性A β 42/A β 40的获得。
The presenilin-containing gamma-secretase complex produces the amyloid beta-peptide (A beta) through intramembrane proteolysis, and >100 presenilin mutations are associated with familial early-onset Alzheimer disease (AD). The question of whether these mutations result in AD through a gain or a loss of function remains highly controversial. Mutations in presenilins increase ratios of 42- to 40-residue A beta critical to pathogenesis, but other A beta s of 38 - 49 residues are also formed by gamma-secretase. Evidence in cells suggests the protease first cleaves substrate within the transmembrane domain at the E site to form 48- or 49-residue A beta. Subsequent cleavage almost every three residues from the C terminus is thought to occur along two pathways toward shorter secreted forms of A beta: A beta 49 -> A beta 46 -> A beta 43 -> A beta 40 and A beta 48 -> A beta 45 -> A beta 42 -> A beta 38. Here we show that the addition of synthetic long A beta peptides (A beta 45- 49) directly into purified preparations of gamma-secretase leads to the formation of A beta 40 and A beta 42 whether the protease complex is detergent-solubilized or reconstituted into lipid vesicles, and the ratios of products A beta 42 to A beta 40 follow a pattern consistent with the dual-pathway hypothesis. Kinetic analysis of five different AD-causing mutations in presenilin-1 revealed that all result in drastic reduction of normal carboxypeptidase function. Altered trimming of long A beta peptides to A beta 40 and A beta 42 by mutant proteases occurs at multiple levels, independent of the effects on initial endoproteolysis at the E site, all conspiring to increase the critical A beta 42/A beta 40 ratio implicated in A beta pathogenesis. Taken together, these results suggest that specific reduction of carboxypeptidase function of gamma-secretase leads to the gain of toxic A beta 42/A beta 40.