Bernasconi D, Schultz U, Staeheli P
Institut für Mikrobiologie und Hygiene, Abteilung Virologie, University of Freiburg, Germany.
J Interferon Cytokine Res. 1995 Jan;15(1):47-53. doi: 10.1089/jir.1995.15.47.
cDNA sequencing revealed that chick Mx protein consists of 705 amino acids. Its 84 N-terminal amino acids show no significant sequence homology to other Mx proteins. They are followed by 514 residues that include a tripartite GTP binding consensus motif. This region shows 50-70% sequence identity to mammalian and duck Mx proteins. Sequences near the C terminus, including a leucine zipper motif, are also conserved, whereas the intervening 19 amino acids lack sequence similarity. This unique sequence corresponds to a highly variable region in mammalian Mx proteins, suggesting that it serves as a spacer between functional domains. Chick and mouse cells transiently transfected with cDNA expression constructs synthesized chick Mx protein at a level that could easily be detected with specific antibodies. Chick Mx protein in such cells was mainly cytoplasmic and had a granular appearance. Permanently transfected cell lines expressing high levels of chick Mx protein could not be established, suggesting low metabolic stability of chick Mx protein or incompatibility with cell proliferation. The antiviral activity of chick Mx protein was tested at the single-cell level using immunofluorescence techniques. Transfected cells expressing chick Mx protein showed no enhanced resistance to influenza A virus, vesicular stomatitis virus, Thogoto virus, or Sendai virus. Thus, chick Mx joins the list of Mx proteins without recognized antiviral activity, supporting the concept that Mx proteins serve unrelated functions.
cDNA测序显示，鸡Mx蛋白由705个氨基酸组成。其N端的84个氨基酸与其他Mx蛋白没有明显的序列同源性。随后是514个残基，其中包括一个三联体GTP结合共有基序。该区域与哺乳动物和鸭Mx蛋白的序列同一性为50-70%。C端附近的序列，包括亮氨酸拉链基序，也具有保守性，而中间的19个氨基酸缺乏序列相似性。这一独特序列对应于哺乳动物Mx蛋白中的一个高度可变区域，表明它作为功能域之间的间隔区。用cDNA表达构建体瞬时转染的鸡和小鼠细胞以一种能用特异性抗体轻松检测到的水平合成了鸡Mx蛋白。此类细胞中的鸡Mx蛋白主要位于细胞质中，呈颗粒状外观。无法建立表达高水平鸡Mx蛋白的永久转染细胞系，这表明鸡Mx蛋白代谢稳定性低或与细胞增殖不兼容。使用免疫荧光技术在单细胞水平上测试了鸡Mx蛋白的抗病毒活性。表达鸡Mx蛋白的转染细胞对甲型流感病毒、水疱性口炎病毒、托戈托病毒或仙台病毒没有增强的抗性。因此，鸡Mx加入了没有公认抗病毒活性的Mx蛋白列表，支持了Mx蛋白具有不相关功能的概念。
