Ubiquitylation is required for degradation of transmembrane surface proteins in trypanosomes
Ubiquitylation is required for degradation of transmembrane surface proteins in trypanosomes
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DOI：
10.1111/j.1600-0854.2008.00785.x
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发表时间：
2008-10-01
期刊：
影响因子：
4.5
通讯作者：
Field, Mark C.
中科院分区：
文献类型：
--
作者：
Chung, Wei-Lian;Leung, Ka Fai;Field, Mark C.
布鲁氏锥虫的表面以糖基磷脂酰肌醇（GPI）锚定蛋白为主，内吞作用依赖于网格蛋白。绝大多数内化的gpi锚定蛋白被有效地回收利用，而跨膜结构域（TMD）蛋白被内化和分类的过程尚不清楚。我们证明了不变表面糖蛋白（ISG）65（一种锥虫TMD蛋白）的内化涉及泛素化，也需要网格蛋白。我们发现细胞质赖氨酸残基在内化和转化过程中具有层次要求，并且单个位置特异性赖氨酸足以降解，表面去除和低聚泛素链的附着。泛素化依赖于上下文，因为通过神经元前体细胞表达的发育下调蛋白（NEDD）8的c端融合提供额外的赖氨酸残基不能支持泛素化。NEDD8的附着通过第二种不依赖泛素的途径导致降解。此外，泛素化或泛素化底物的降解发生在酸性室中，并且与蛋白质体无关。值得注意的是，在非opisthokont谱系中，Rsp5p或c-Cbl，作用于内吞货物的E3泛素连接酶不存在，但Uba1类基因存在，并且是细胞活力和ISG65泛素化所必需的。因此，泛素化是一种表面蛋白内化的进化保守机制，但该机制在主要真核生物谱系之间存在很大差异。
The surface of Trypanosoma brucei is dominated by glycosyl-phosphatidylinositol (GPI)-anchored proteins, and endocytosis is clathrin dependent. The vast majority of internalized GPI-anchored protein is efficiently recycled, while the processes by which transmembrane domain (TMD) proteins are internalized and sorted are unknown. We demonstrate that internalization of invariant surface glycoprotein (ISG)65, a trypanosome TMD protein, involves ubiquitylation and also requires clathrin. We find a hierarchical requirement for cytoplasmic lysine residues in internalization and turnover, and a single position-specific lysine is sufficient for degradation, surface removal and attachment of oligoubiquitin chains. Ubiquitylation is context dependent as provision of additional lysine residues by C-terminal fusion of neuronal precursor cell-expressed developmentally downregulated protein (NEDD)8 fails to support ubiquitylation. Attachment of NEDD8 leads to degradation by a second ubiquitin-independent pathway. Moreover, degradation of ubiquitylated or NEDDylated substrate takes place in an acidic compartment and is proteosome independent. Significantly, in non-opisthokont lineages, Rsp5p or c-Cbl, the E3 ubiquitin ligases acting on endocytic cargo, are absent but Uba1 class genes are present and are required for cell viability and ISG65 ubiquitylation. Hence, ubiquitylation is an evolutionarily conserved mechanism for internalization of surface proteins, but aspects of the machinery differ substantially between the major eukaryotic lineages.