Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Biol Cell. 2012 Jun;23(12):2339-51. doi: 10.1091/mbc.E11-11-0944. Epub 2012 May 2.
The β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease that catalyzes the proteolytic processing of APP and other plasma membrane protein precursors. BACE1 cycles between the trans-Golgi network (TGN), the plasma membrane, and endosomes by virtue of signals contained within its cytosolic C-terminal domain. One of these signals is the DXXLL-motif sequence DISLL, which controls transport between the TGN and endosomes via interaction with GGA proteins. Here we show that the DISLL sequence is embedded within a longer [DE]XXXL[LI]-motif sequence, DDISLL, which mediates internalization from the plasma membrane by interaction with the clathrin-associated, heterotetrameric adaptor protein 2 (AP-2) complex. Mutation of this signal or knockdown of either AP-2 or clathrin decreases endosomal localization and increases plasma membrane localization of BACE1. Remarkably, internalization-defective BACE1 is able to cleave an APP mutant that itself cannot be delivered to endosomes. The drug brefeldin A reversibly prevents BACE1-catalyzed APP cleavage, ruling out that this reaction occurs in the endoplasmic reticulum (ER) or ER-Golgi intermediate compartment. Taken together, these observations support the notion that BACE1 is capable of cleaving APP in late compartments of the secretory pathway.
β-淀粉样前体蛋白(APP)裂解酶 1(BACE1)是一种跨膜天冬氨酸蛋白酶,可催化 APP 和其他质膜蛋白前体的蛋白水解加工。BACE1 通过其胞质 C 末端结构域中的信号在转高尔基网络(TGN)、质膜和内体之间循环。这些信号之一是 DXXLL 基序序列 DISLL,它通过与 GGA 蛋白相互作用控制 TGN 和内体之间的运输。在这里,我们表明 DISLL 序列嵌入在更长的 [DE]XXXL[LI]-基序序列 DDISLL 中,该序列通过与网格蛋白相关的异四聚体衔接蛋白 2(AP-2)复合物相互作用介导从质膜内化。该信号的突变或 AP-2 或网格蛋白的敲低会减少内体定位并增加 BACE1 的质膜定位。值得注意的是,内化缺陷的 BACE1 能够切割自身不能递送至内体的 APP 突变体。药物布雷菲德菌素 A 可逆地阻止 BACE1 催化的 APP 裂解,排除该反应发生在内质网(ER)或 ER-高尔基体中间隔室中。综上所述,这些观察结果支持 BACE1 能够在分泌途径的晚期隔室中切割 APP 的观点。