Mannose Trimming Is Required for Delivery of a Glycoprotein from EDEM1 to XTP3-B and to Late Endoplasmic Reticulum-associated Degradation Steps
Mannose Trimming Is Required for Delivery of a Glycoprotein from EDEM1 to XTP3-B and to Late Endoplasmic Reticulum-associated Degradation Steps
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DOI：
10.1074/jbc.m110.154849
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发表时间：
2011-01-14
影响因子：
4.8
通讯作者：
Lederkremer, Gerardo Z.
中科院分区：
文献类型：
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作者：
Groisman, Bella;Shenkman, Marina;Lederkremer, Gerardo Z.
虽然从前体N-连接寡糖中修剪α 1，2-甘露糖残基是将错误折叠的糖蛋白递送至内质网（ER）相关降解（ERAD）的重要步骤，但这种修剪的确切作用尚不清楚。最初认为EDEM 1在甘露糖修剪后结合N-聚糖，目前认为这是凝集素OS 9和XTP 3-B的作用，因为它们对修剪的寡糖具有体外亲和力。我们之前已经表明，ER甘露糖苷酶I（ERManI）是修整所需的，并与ERAD底物和ERAD机器一起浓缩在中心粒周围ER衍生的质量控制室（ERQC）中。甘露糖修剪的抑制防止ERQC中的底物积累。在这里，我们表明，甘露糖苷酶抑制剂kifunensine或ERManI敲低不影响ERAD底物糖蛋白结合EDEM 1。相反，底物与XTP 3-B和E3泛素连接酶HRD 1和SCFFbs 2的结合受到抑制。一致的是，而ERAD底物部分共定位后，蛋白酶体抑制与EDEM 1，HRD 1，和Fbs 2在ERQC，共定位抑制甘露糖苷酶抑制的情况下，E3连接酶，但不为EDEM 1。有趣的是，与Derlin-1的底物的缔合和共定位独立于甘露糖修剪。HRD 1衔接蛋白SEL 1 L在向OS 9和XTP 3-B的N-聚糖依赖性底物递送中发挥作用。然而，底物与XTP 3-B的结合仍然依赖于SEL 1 L敲低后的甘露糖修剪。我们的研究结果表明，甘露糖修剪能够通过与XTP 3-B的关联将底物糖蛋白从EDEM 1递送到晚期ERAD步骤。
Although the trimming of alpha 1,2-mannose residues from precursor N-linked oligosaccharides is an essential step in the delivery of misfolded glycoproteins to endoplasmic reticulum (ER)-associated degradation (ERAD), the exact role of this trimming is unclear. EDEM1 was initially suggested to bind N-glycans after mannose trimming, a role presently ascribed to the lectins OS9 and XTP3-B, because of their in vitro affinities for trimmed oligosaccharides. We have shown before that ER mannosidase I (ERManI) is required for the trimming and concentrates together with the ERAD substrate and ERAD machinery in the pericentriolar ER-derived quality control compartment (ERQC). Inhibition of mannose trimming prevents substrate accumulation in the ERQC. Here, we show that the mannosidase inhibitor kifunensine or ERManI knockdown do not affect binding of an ERAD substrate glycoprotein to EDEM1. In contrast, substrate association with XTP3-B and with the E3 ubiquitin ligases HRD1 and SCFFbs2 was inhibited. Consistently, whereas the ERAD substrate partially colocalized upon proteasomal inhibition with EDEM1, HRD1, and Fbs2 at the ERQC, colocalization was repressed by mannosidase inhibition in the case of the E3 ligases but not for EDEM1. Interestingly, association and colocalization of the substrate with Derlin-1 was independent of mannose trimming. The HRD1 adaptor protein SEL1L had been suggested to play a role in N-glycan-dependent substrate delivery to OS9 and XTP3-B. However, substrate association with XTP3-B was still dependent on mannose trimming upon SEL1L knockdown. Our results suggest that mannose trimming enables delivery of a substrate glycoprotein from EDEM1 to late ERAD steps through association with XTP3-B.