Maeda J, Repass J F, Maeda A, Makino S
Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, Texas 77555, USA.
Virology. 2001 Mar 15;281(2):163-9. doi: 10.1006/viro.2001.0818.
Coronavirus small envelope protein E has two known biological functions: it plays a pivotal role in virus envelope formation, and the murine coronavirus E protein induces apoptosis in E protein-expressing cultured cells. The E protein is an integral membrane protein. Its C-terminal region extends cytoplasmically in the infected cell and in the virion toward the interior. The N-terminal two-thirds of the E protein is hydrophobic and lies buried within the membrane, but its orientation in the lipid membrane is not known. Immunofluorescent analyses of cells expressing biologically active murine coronavirus E protein with a hydrophilic short epitope tag at the N-terminus showed that the epitope tag was exposed cytoplasmically. Immunoprecipitation analyses of the purified microsomal membrane vesicles that contain the same tagged E protein revealed the N-terminal epitope tag outside the microsomal membrane vesicles. These analyses demonstrated that the epitope tag at the N-terminus of the E protein was exposed cytoplasmically. Our data were consistent with an E protein topology model, in which the N-terminal two-thirds of the transmembrane domain spans the lipid bilayer twice, exposing the C-terminal region to the cytoplasm or virion interior.
冠状病毒小包膜蛋白E具有两种已知的生物学功能：它在病毒包膜形成中起关键作用，并且鼠冠状病毒E蛋白可在表达E蛋白的培养细胞中诱导凋亡。E蛋白是一种整合膜蛋白。其C末端区域在受感染细胞和病毒粒子中向细胞质内部延伸。E蛋白的N末端三分之二是疏水的，埋在膜内，但其在脂质膜中的方向尚不清楚。对在N末端带有亲水性短表位标签的表达具有生物活性的鼠冠状病毒E蛋白的细胞进行免疫荧光分析，结果表明表位标签暴露于细胞质中。对含有相同标记E蛋白的纯化微粒体膜囊泡进行免疫沉淀分析，发现在微粒体膜囊泡外部存在N末端表位标签。这些分析表明，E蛋白N末端的表位标签暴露于细胞质中。我们的数据与E蛋白拓扑模型一致，在该模型中，跨膜结构域的N末端三分之二跨脂质双层两次，使C末端区域暴露于细胞质或病毒粒子内部。
