Fbs2 is a new member of the E3 ubiquitin ligase family that recognizes sugar chains
Fbs2 is a new member of the E3 ubiquitin ligase family that recognizes sugar chains
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DOI：
10.1074/jbc.m304157200
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发表时间：
2003-10-31
影响因子：
4.8
通讯作者：
Tai, T
中科院分区：
文献类型：
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作者：
Yoshida, Y;Tokunaga, F;Tai, T
F-box蛋白是Skp 1-Cullin 1-F-box蛋白-Roc 1（SCF）E3泛素蛋白连接酶的底物识别组分。我们先前报道了Fbs 1（识别糖链的F-box蛋白;相当于Fbx 2或NFB 42）特异性结合与高甘露糖寡糖连接的蛋白，随后有助于消除胞质溶胶中的N-糖蛋白（Yoshida，Y.，千叶，T.，Tokunaga，F.，川崎，H. Iwai，K.，铃木，T.，伊藤，Y.，Matsuoka，K.，Yoshida，M.，田中，K.，Tai，T.（2002）Nature 418，438 - 442）。在这里，我们报告了另一种识别N-聚糖的F-box蛋白Fbs 2（以前称为Fbx 6 b或FBG 2）的鉴定。虽然Fbs 1的表达仅限于成年大脑和睾丸，但Fbs 2转录本广泛表达。Fbs 2蛋白形成SCFFbs 2泛素-连接酶复合物，其靶向N-糖蛋白中的糖链进行泛素化。只有糖蛋白结合刀豆球蛋白A凝集素，而不是麦胚凝集素或蓖麻凝集素与Fbs 2在各种组织和细胞系。使用各种寡糖的下拉分析显示，Man（3-9）GlcNAc（2）聚糖是有效结合Fbs 2所必需的，而通过其他糖修饰甘露糖残基或缺失内部GlcNAc会降低Fbs 2结合。Fbs 2与T细胞受体α亚基（TCR α）的N-聚糖（内质网相关降解（ERAD）途径的典型底物）相互作用，以及缺乏形成SCF复合物所必需的F-box结构域的突变型Fbs 2 DeltaF的强制表达，以及小干扰RNA对内源性Fbs 2的减少导致细胞中TCR α降解的抑制。因此，Fbs 2是F-box蛋白家族的新成员，其识别N-聚糖并在ERAD中起作用。
F-box proteins are substrate recognition components of Skp1-Cullin1-F-box protein-Roc1 (SCF) E3 ubiquitin-protein ligases. We reported previously that Fbs1 (F-box protein that recognizes sugar chains; equivalent to Fbx2 or NFB42) binds specifically to proteins attached with high mannose oligosaccharides and subsequently contributes to elimination of N-glycoproteins in cytosol (Yoshida, Y., Chiba, T., Tokunaga, F., Kawasaki, H., Iwai, K., Suzuki, T., Ito, Y., Matsuoka, K., Yoshida, M., Tanaka, K., and Tai, T. (2002) Nature 418, 438 - 442). Here we report the identification of another F-box protein that recognizes N-glycan, Fbs2 (called Fbx6b or FBG2 previously). Although the expression of Fbs1 was restricted to the adult brain and testis, the Fbs2 transcript was widely expressed. The Fbs2 protein forms an SCFFbs2 ubiquitin-ligase complex that targets sugar chains in N-glycoproteins for ubiquitylation. Only glycoproteins bound to concanavalin A lectin and not to wheat germ agglutinin or Ricinus communis agglutinin interacted with Fbs2 in various tissues and cell lines. Pull-down analysis using various oligosaccharides revealed that Man(3-9)GlcNAc(2) glycans were required for efficient Fbs2 binding, whereas modifications of mannose residues by other sugars or deletion of inner GlcNAc reduced Fbs2 binding. Fbs2 interacted with N-glycans of T-cell receptor alpha-subunit (TCRalpha), a typical substrate of the endoplasmic reticulum-associated degradation (ERAD) pathway, and the forced expression of mutant Fbs2DeltaF, which lacks the F-box domain essential for forming the SCF complex, and decrease of endogenous Fbs2 by small interfering RNA led to inhibition of TCRalpha degradation in cells. Thus, Fbs2 is a novel member of F-box protein family that recognizes N-glycans and plays a role in ERAD.