Phosphorylation of both phosphoacceptor sites in the HIV-1 Vpu cytoplasmic domain is essential for Vpu-mediated ER degradation of CD4
Phosphorylation of both phosphoacceptor sites in the HIV-1 Vpu cytoplasmic domain is essential for Vpu-mediated ER degradation of CD4
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DOI：
10.1006/viro.1997.8541
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发表时间：
1997-05-26
期刊：
影响因子：
3.7
通讯作者：
Jabbar, MA
中科院分区：
文献类型：
--
作者：
Paul, M;Jabbar, MA
人类免疫缺陷病毒1型（HIV-1） Vpu在54-aa细胞质结构域酸性十二肽区存在的两个丝氨酸残基（Ser52和Ser56）上磷酸化。先前的实验表明，Vpu磷酸化对内质网中CD4的降解至关重要。在这项研究中，我们进行了实验来阐明单个磷受体位点在CD4蛋白水解中的作用。我们发现酸性氨基酸不能在功能上替代Vpu中能够诱导CD4降解的磷酸丝氨酸。我们的研究进一步表明，两个磷酸化受体位点中的任何一个磷酸化都不足以产生功能性Vpu蛋白。当进行功能性互补测试时，无活性磷酸化精通的Vpu突变体无法产生能够诱导Vpu敏感糖蛋白降解的Vpu蛋白。补体的失败不是由于Vpu蛋白的组装缺陷，因为未磷酸化的Vpu在细胞中形成了寡聚复合物。我们还发现Vpu的表达以磷酸化依赖的方式抑制蛋白转运。因此，我们的研究表明，Vpu中的两种磷酸丝氨酸都是导致内质网中CD4蛋白水解途径的关键参与者，并且这些磷酸丝氨酸应该存在于Vpu蛋白的同一亚基上。(C) 1997学术出版社。
Human immunodeficiency virus type 1 (HIV-1) Vpu is phosphorylated at two serine residues (Ser52 and Ser56) present within the acidic dodecapeptide region of the 54-aa cytoplasmic domain. Previous experiments have shown that Vpu phosphorylation is critical for the degradation of CD4 in the endoplasmic reticulum. In this study, we carried out experiments to elucidate the role of individual phosphoacceptor sites in CD4 proteolysis. We show here that acidic amino acids could not functionally substitute for phosphoserines in Vpu that is capable of inducing the degradation of CD4. Our studies have further revealed that phosphorylation of either of the two phosphoacceptor sites is not sufficient to generate a functional Vpu protein. When tested for functional complementation, inactive phosphorylation-proficient Vpu mutants failed to generate Vpu proteins that had the ability to induce the degradation of Vpu-sensitive glycoproteins. The failure to complement was not due to assembly defects in the Vpu protein as unphosphorylated Vpu formed oligomeric complexes in the cell. We also showed that Vpu expression inhibits protein transport in a phosphorylation-dependent manner. Our studies have thus revealed that both phosphoserines in Vpu are critical participants in a pathway that leads to the proteolysis of CD4 in the ER and that these phosphoserines should be present on the same subunit of the Vpu protein. (C) 1997 Academic Press.