Structural basis of sugar-recognizing ubiquitin ligase
Structural basis of sugar-recognizing ubiquitin ligase
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DOI：
10.1038/nsmb732
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发表时间：
2004-04-01
影响因子：
16.8
通讯作者：
Tanaka, K
中科院分区：
文献类型：
--
作者：
Mizushima, T;Hirao, T;Tanaka, K
SCFFbs1是一种泛素连接酶，参与内质网(ER)相关的降解途径。Fbs1/Fbx2是F-box蛋白的一员，识别高甘露糖低聚糖。有效地结合N-糖链需要二-N-乙酰基壳二糖(壳二糖)。本文报道了Fbs1的糖结合域(SBD)及其与壳二糖的复合体的晶体结构。SBD由十链反平行的β-三明治组成。SBD壳二糖复合体的结构包括Fbs1和壳二糖之间的氢键以及壳二糖的甲基插入Fbs1的一个小的疏水口袋中。此外，核磁共振波谱还表明，与壳二糖结合部位相邻的氨基酸残基与碳水化合物部分的外支相互作用。考虑到N-糖链中最内侧的壳二糖部分通常参与与多肽部分的分子内相互作用，我们认为Fbs1与未折叠N-糖蛋白中的壳二糖相互作用，使蛋白质部分指向E2泛素化。
SCFFbs1 is a ubiquitin ligase that functions in the endoplasmic reticulum (ER)-associated degradation pathway. Fbs1/Fbx2, a member of the F-box proteins, recognizes high-mannose oligosaccharides. Efficient binding to an N-glycan requires di-N-acetylchitobiose ( chitobiose). Here we report the crystal structures of the sugar-binding domain (SBD) of Fbs1 alone and in complex with chitobiose. The SBD is composed of a ten-stranded antiparallel beta-sandwich. The structure of the SBD chitobiose complex includes hydrogen bonds between Fbs1 and chitobiose and insertion of the methyl group of chitobiose into a small hydrophobic pocket of Fbs1. Moreover, NMR spectroscopy has demonstrated that the amino acid residues adjoining the chitobiose-binding site interact with the outer branches of the carbohydrate moiety. Considering that the innermost chitobiose moieties in N-glycans are usually involved in intramolecular interactions with the polypeptide moieties, we propose that Fbs1 interacts with the chitobiose in unfolded N-glycoprotein, pointing the protein moiety toward E2 for ubiquitination.