Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA; Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
Cell. 2019 Apr 18;177(3):737-750.e15. doi: 10.1016/j.cell.2019.03.035.
The proteasome mediates selective protein degradation and is dynamically regulated in response to proteotoxic challenges. SKN-1A/Nrf1, an endoplasmic reticulum (ER)-associated transcription factor that undergoes N-linked glycosylation, serves as a sensor of proteasome dysfunction and triggers compensatory upregulation of proteasome subunit genes. Here, we show that the PNG-1/NGLY1 peptide:N-glycanase edits the sequence of SKN-1A protein by converting particular N-glycosylated asparagine residues to aspartic acid. Genetically introducing aspartates at these N-glycosylation sites bypasses the requirement for PNG-1/NGLY1, showing that protein sequence editing rather than deglycosylation is key to SKN-1A function. This pathway is required to maintain sufficient proteasome expression and activity, and SKN-1A hyperactivation confers resistance to the proteotoxicity of human amyloid beta peptide. Deglycosylation-dependent protein sequence editing explains how ER-associated and cytosolic isoforms of SKN-1 perform distinct cytoprotective functions corresponding to those of mammalian Nrf1 and Nrf2. Thus, we uncover an unexpected mechanism by which N-linked glycosylation regulates protein function and proteostasis.
蛋白酶体介导选择性蛋白质降解，并能动态响应于蛋白质毒性挑战进行调节。SKN-1A/Nrf1 是一种内质网（ER）相关的转录因子，它经历 N 连接糖基化，作为蛋白酶体功能障碍的传感器，触发蛋白酶体亚基基因的代偿性上调。在这里，我们表明 PNG-1/NGLY1 肽：N-糖基化酶通过将特定的 N-糖基化天冬酰胺残基转化为天冬氨酸来编辑 SKN-1A 蛋白的序列。在这些 N-糖基化位点引入天冬氨酸可以绕过对 PNG-1/NGLY1 的需求，表明蛋白序列编辑而不是去糖基化是 SKN-1A 功能的关键。该途径对于维持足够的蛋白酶体表达和活性是必需的，并且 SKN-1A 的过度激活赋予了对人类淀粉样β肽的蛋白质毒性的抗性。依赖于去糖基化的蛋白序列编辑解释了 ER 相关和胞质型 SKN-1 如何执行与哺乳动物 Nrf1 和 Nrf2 相对应的不同细胞保护功能。因此，我们揭示了 N 连接糖基化调节蛋白功能和蛋白稳态的一种意外机制。
