Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany.
School of Chemistry and Molecular Biosciences, ARC Training Centre for Biopharmaceutical Innovation, The University of Queensland, St Lucia, QLD 4072, Australia.
J Cell Sci. 2020 Mar 26;133(6):jcs243790. doi: 10.1242/jcs.243790.
The endoplasmic reticulum (ER)-resident intramembrane rhomboid protease RHBDL4 generates metastable protein fragments and together with the ER-associated degradation (ERAD) machinery provides a clearance mechanism for aberrant and surplus proteins. However, the endogenous substrate spectrum and with that the role of RHBDL4 in physiological ERAD is mainly unknown. Here, we use a substrate trapping approach in combination with quantitative proteomics to identify physiological RHBDL4 substrates. This revealed oligosaccharyltransferase (OST) complex subunits such as the catalytic active subunit STT3A as substrates for the RHBDL4-dependent ERAD pathway. RHBDL4-catalysed cleavage inactivates OST subunits by triggering dislocation into the cytoplasm and subsequent proteasomal degradation. RHBDL4 thereby controls the abundance and activity of OST, suggesting a novel link between the ERAD machinery and glycosylation tuning.
内质网（ER）驻留的跨膜丝氨酸蛋白酶 RHBDL4 产生亚稳态蛋白片段，与 ER 相关降解（ERAD）机制一起为异常和多余的蛋白质提供了清除机制。然而，RHBDL4 在内质网生理 ERAD 中的内源性底物谱及其作用主要是未知的。在这里，我们使用底物捕获方法结合定量蛋白质组学来鉴定生理 RHBDL4 底物。这揭示了寡糖基转移酶（OST）复合物亚基，如催化活性亚基 STT3A，是 RHBDL4 依赖的 ERAD 途径的底物。RHBDL4 催化的切割通过触发向细胞质易位并随后进行蛋白酶体降解来使 OST 亚基失活。RHBDL4 因此控制 OST 的丰度和活性，这表明 ERAD 机制和糖基化调节之间存在新的联系。
