Glozman Rina, Okiyoneda Tsukasa, Mulvihill Cory M, Rini James M, Barriere Herve, Lukacs Gergely L
Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario, Canada.
J Cell Biol. 2009 Mar 23;184(6):847-62. doi: 10.1083/jcb.200808124.
N-glycosylation, a common cotranslational modification, is thought to be critical for plasma membrane expression of glycoproteins by enhancing protein folding, trafficking, and stability through targeting them to the ER folding cycles via lectin-like chaperones. In this study, we show that N-glycans, specifically core glycans, enhance the productive folding and conformational stability of a polytopic membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), independently of lectin-like chaperones. Defective N-glycosylation reduces cell surface expression by impairing both early secretory and endocytic traffic of CFTR. Conformational destabilization of the glycan-deficient CFTR induces ubiquitination, leading to rapid elimination from the cell surface. Ubiquitinated CFTR is directed to lysosomal degradation instead of endocytic recycling in early endosomes mediated by ubiquitin-binding endosomal sorting complex required for transport (ESCRT) adaptors Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and TSG101. These results suggest that cotranslational N-glycosylation can exert a chaperone-independent profolding change in the energetic of CFTR in vivo as well as outline a paradigm for the peripheral trafficking defect of membrane proteins with impaired glycosylation.
N-糖基化是一种常见的共翻译修饰，被认为通过凝集素样伴侣将糖蛋白靶向内质网折叠循环，从而增强蛋白质折叠、运输和稳定性，对糖蛋白的质膜表达至关重要。在本研究中，我们表明N-聚糖，特别是核心聚糖，独立于凝集素样伴侣增强了多聚体膜蛋白囊性纤维化跨膜电导调节因子（CFTR）的有效折叠和构象稳定性。有缺陷的N-糖基化通过损害CFTR的早期分泌和内吞运输来降低细胞表面表达。聚糖缺陷型CFTR的构象不稳定诱导泛素化，导致其从细胞表面快速清除。泛素化的CFTR被导向溶酶体降解，而不是在由泛素结合内体分选复合物运输所需的（ESCRT）衔接蛋白Hrs（肝细胞生长因子调节的酪氨酸激酶底物）和TSG101介导的早期内体中进行内吞再循环。这些结果表明，共翻译N-糖基化在体内可对CFTR的能量产生一种不依赖伴侣的促折叠变化，并勾勒出糖基化受损的膜蛋白外周运输缺陷的范例。
