Coscoy L, Sanchez D J, Ganem D
Howard Hughes Medical Institute and Department of Microbiology, University of California Medical Center, San Francisco, CA 94143, USA.
J Cell Biol. 2001 Dec 24;155(7):1265-73. doi: 10.1083/jcb.200111010.
Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells. This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins. Here, we show that expression of MIR1 and MIR2 leads to ubiquitination of the cytosolic tail of their target proteins and that ubiquitination is essential for their removal from the cell surface. MIR1 and MIR2 both contain cytosolic zinc fingers of the PHD subfamily, and these structures are required for this activity. In vitro, addition of a MIR2-glutathione S-transferase (GST) fusion protein to purified E1 and E2 enzymes leads to transfer of ubiquitin (Ub) to GST-containing targets in an ATP- and E2-dependent fashion; this reaction is abolished by mutation of the Zn-coordinating residues of the PHD domain. Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.
卡波西肉瘤相关疱疹病毒编码两种跨膜蛋白（免疫识别调节因子[MIR]1和MIR2），它们可下调参与感染细胞免疫识别的细胞表面分子（主要组织相容性复合体I类分子、B7.2和细胞间黏附分子1）。这种下调是由于靶蛋白的内吞作用增强以及随后在内溶酶体中的降解所致。在此，我们表明MIR1和MIR2的表达会导致其靶蛋白胞质尾的泛素化，并且泛素化对于它们从细胞表面的去除至关重要。MIR1和MIR2均含有PHD亚家族的胞质锌指，这些结构对于此活性是必需的。在体外，将MIR2-谷胱甘肽S-转移酶（GST）融合蛋白添加到纯化的E1和E2酶中会导致泛素（Ub）以ATP和E2依赖的方式转移到含GST的靶标上；该反应因PHD结构域锌配位残基的突变而被消除。因此，MIR2定义了一类新型的膜结合E3泛素连接酶，其可调节宿主细胞膜蛋白的运输。
