Nakayama M, Yazaki K, Kusano A, Nagata K, Hanai N, Ishihama A
Department of Molecular Genetics, National Institute of Genetics, Shizuoka, Japan.
J Biol Chem. 1993 Jul 15;268(20):15033-8.
Mouse Mx1 protein is an interferon-inducible nuclear protein and confers resistance to influenza virus infection. The Mx1 protein purified from interferon-induced A2G mouse liver exhibited GTPase activity as did the Mx1 protein purified from the Mx1 cDNA-expressing Escherichia coli (Nakayama, M., Nagata, K., Kato, A., and Ishihama, A. (1991) J. Biol. Chem. 266, 21404-21408; Nakayama, M., Nagata, K., and Ishihama, A. (1992) Virus Res. 22, 227-234). The Mx1 protein purified from both mouse liver and Mx1-cDNA expressing E. coli was found to exist as assembled polymeric states judged from gel filtration pattern. By making a set of deletion derivatives of the Mx1 cDNA, the main motif for self-assembly of the Mx1 protein was mapped between amino acid residues 51-99. This motif is highly conserved not only in the Mx family of proteins but also in Mx-related proteins. The polymeric form of Mx1 from E. coli was observed as "horseshoe"-like structure by negative staining microscopy. When the Mx1 protein was incubated with GTP, this horseshoe structure was transformed to larger and tightly stacked helical forms. Electron microscopic analysis of immunostained liver of the interferon-induced mice indicated that the Mx1 protein exists in nuclei, forming giant complexes of about half the size of nucleoli.
小鼠Mx1蛋白是一种干扰素诱导的核蛋白，可赋予对流感病毒感染的抗性。从干扰素诱导的A2G小鼠肝脏中纯化的Mx1蛋白表现出GTPase活性，从表达Mx1 cDNA的大肠杆菌中纯化的Mx1蛋白也表现出该活性（中山，M.，永田，K.，加藤，A.，和石滨，A.（1991）《生物化学杂志》266，21404 - 21408；中山，M.，永田，K.，和石滨，A.（1992）《病毒研究》22，227 - 234）。从小鼠肝脏和表达Mx1 - cDNA的大肠杆菌中纯化的Mx1蛋白，根据凝胶过滤图谱判断，发现其以组装的聚合物状态存在。通过构建一组Mx1 cDNA的缺失衍生物，确定了Mx1蛋白自我组装的主要基序位于氨基酸残基51 - 99之间。该基序不仅在Mx蛋白家族中高度保守，在与Mx相关的蛋白中也高度保守。通过负染色显微镜观察，来自大肠杆菌的Mx1聚合物形式呈现为“马蹄形”结构。当Mx1蛋白与GTP一起孵育时，这种马蹄形结构转变为更大且紧密堆积的螺旋形式。对干扰素诱导小鼠的免疫染色肝脏进行电子显微镜分析表明，Mx1蛋白存在于细胞核中，形成约为核仁大小一半的巨大复合物。
