PDF(Pubmed)
Abstract：
Autophagy mediates the degradation of intracellular macromolecules and organelles within lysosomes. There are three types of autophagy: macroautophagy, microautophagy, and chaperone-mediated autophagy. Heat shock protein 70.1 (Hsp70.1) exhibits dual functions as a chaperone protein and a lysosomal membrane stabilizer. Since chaperone-mediated autophagy participates in the recycling of ∼30% cytosolic proteins, its disorder causes cell susceptibility to stress conditions. Cargo proteins destined for degradation such as amyloid precursor protein and tau protein are trafficked by Hsp70.1 from the cytosol into lysosomes. Hsp70.1 is composed of an N-terminal nucleotide-binding domain (NBD) and a C-terminal domain that binds to cargo proteins, termed the substrate-binding domain (SBD). The NBD and SBD are connected by the interdomain linker LL1, which modulates the allosteric structure of Hsp70.1 in response to ADP/ATP binding. After the passage of the Hsp70.1-cargo complex through the lysosomal limiting membrane, high-affinity binding of the positive-charged SBD with negative-charged bis(monoacylglycero)phosphate (BMP) at the internal vesicular membranes activates acid sphingomyelinase to generate ceramide for stabilizing lysosomal membranes. As the integrity of the lysosomal limiting membrane is critical to ensure cargo protein degradation within the acidic lumen, the disintegration of the lysosomal limiting membrane is lethal to cells. After the intake of high-fat diets, however, β-oxidation of fatty acids in the mitochondria generates reactive oxygen species, which enhance the oxidation of membrane linoleic acids to produce 4-hydroxy-2-nonenal (4-HNE). In addition, 4-HNE is produced during the heating of linoleic acid-rich vegetable oils and incorporated into the body via deep-fried foods. This endogenous and exogenous 4-HNE synergically causes an increase in its serum and organ levels to induce carbonylation of Hsp70.1 at Arg469, which facilitates its conformational change and access of activated μ-calpain to LL1. Therefore, the cleavage of Hsp70.1 occurs prior to its influx into the lysosomal lumen, which leads to lysosomal membrane permeabilization/rupture. The resultant leakage of cathepsins is responsible for lysosomal cell death, which would be one of the causative factors of lifestyle-related diseases.
摘要：
自噬介导溶酶体内细胞内大分子和细胞器的降解。有三种类型的自噬：巨自噬，微自噬,和伴侣介导的自噬。热休克蛋白70.1（Hsp70.1）具有伴侣蛋白和溶酶体膜稳定剂的双重功能。由于伴侣介导的自噬参与了~30%的细胞溶质蛋白的再循环，它的紊乱导致细胞对应激条件的易感性。预定用于降解的货物蛋白如淀粉样蛋白前体蛋白和tau蛋白通过Hsp70.1从胞质溶胶运输到溶酶体中。Hsp70.1由N末端核苷酸结合域（NBD）和与货物蛋白结合的C末端域组成，称为底物结合结构域(SBD)。NBD和SBD通过域间接头LL1连接,其响应于ADP/ATP结合而调节Hsp70.1的变构结构。Hsp70.1货物复合物通过溶酶体限制膜后，带正电荷的SBD与带负电荷的双（单酰基甘油）磷酸盐（BMP）在内囊泡膜上的高亲和力结合激活了酸性鞘磷脂酶，以产生神经酰胺来稳定溶酶体膜。由于溶酶体限制膜的完整性对于确保酸性腔内货物蛋白降解至关重要，溶酶体限制膜的崩解对细胞是致命的。摄入高脂肪饮食后，然而,线粒体中脂肪酸的β氧化产生活性氧，其增强膜亚油酸的氧化以产生4-羟基-2-壬烯醛(4-HNE)。此外,4-HNE是在加热富含亚油酸的植物油过程中产生的，并通过油炸食品掺入体内。这种内源性和外源性4-HNE协同导致其血清和器官水平的增加，从而在Arg469处诱导Hsp70.1的羰基化，这有助于其构象变化和活化的μ-钙蛋白酶进入LL1。因此,Hsp70.1的裂解发生在其流入溶酶体腔之前，这导致溶酶体膜透化/破裂。组织蛋白酶的泄漏导致溶酶体细胞死亡，这将是生活方式相关疾病的致病因素之一。
