DPM1, the catalytic subunit of dolichol-phosphate mannose synthase, is tethered to and stabilized on the endoplasmic reticulum membrane by DPM3
DPM1, the catalytic subunit of dolichol-phosphate mannose synthase, is tethered to and stabilized on the endoplasmic reticulum membrane by DPM3
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DOI：
10.1074/jbc.m511311200
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发表时间：
2006-01-13
影响因子：
4.8
通讯作者：
Kinoshita, T
中科院分区：
文献类型：
--
作者：
Ashida, H;Maeda, Y;Kinoshita, T
多萜醇-磷酸甘露糖（甘露糖）合酶是合成糖基磷脂酰肌醇（GPI）锚、N-聚糖前体、蛋白质O-甘露糖和C-甘露糖所必需的。我们先前鉴定了该酶的第三组分DPM 3，其与DPM 1和DPM 2共纯化。在这里，我们已经建立了突变的中国仓鼠卵巢（CHO）2.38细胞，DPM 3缺陷。CHO2.38细胞对GPI锚定蛋白呈阴性，并且来自这些细胞的微粒体显示出不可检测的ATP合酶活性，表明DPM 3是该酶的必需组分。一个卷曲螺旋结构域附近的C端的DPM 3是重要的拴系DPM 1，催化亚基的酶，内质网膜，因此，是至关重要的酶活性。另一方面，在DPM 3的N-末端部分的两个跨膜区显示没有特异性功能。在没有DPM 3的情况下，DPM 1被蛋白酶体迅速降解。游离的DPM 1与Hsc 70相互作用蛋白（CHIP）的C末端密切相关，CHIP是一种伴侣依赖性E3泛素连接酶，表明DPM 1至少部分被CHIP泛素化。
Dolichol-phosphate mannose (DPM) synthase is required for synthesis of the glycosylphosphatidylinositol (GPI) anchor, N-glycan precursor, protein O-mannose, and C-mannose. We previously identified DPM3, the third component of this enzyme, which was co-purified with DPM1 and DPM2. Here, we have established mutant Chinese hamster ovary (CHO) 2.38 cells that were defective in DPM3. CHO2.38 cells were negative for GPI-anchored proteins, and microsomes from these cells showed no detectable DPM synthase activity, indicating that DPM3 is an essential component of this enzyme. A coiled-coil domain near the C terminus of DPM3 was important for tethering DPM1, the catalytic subunit of the enzyme, to the endoplasmic reticulum membrane and, therefore, was critical for enzyme activity. On the other hand, two transmembrane regions in the N-terminal portion of DPM3 showed no specific functions. DPM1 was rapidly degraded by the proteasome in the absence of DPM3. Free DPM1 was strongly associated with the C terminus of Hsc70-interacting protein (CHIP), a chaperone-dependent E3 ubiquitin ligase, suggesting that DPM1 is ubiquitinated, at least in part, by CHIP.