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亨廷顿舞蹈病致病蛋白氨基端出核序列的研究及其对聚集体的影响

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Keywords: 亨廷顿蛋白,聚集物,胞浆定位相关区域,线粒体,多聚谷氨酰胺

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Abstract:

亨廷顿舞蹈病是一种常染色体显性遗传的神经变性疾病.其致病基因为IT15,其编码的蛋白为亨廷顿蛋白.IT15基因1号外显子含有多态性三核苷酸(胞嘧啶-腺嘌呤-鸟嘌呤(CAG))重复序列,当CAG重复拷贝数大于37时引起发病.亨廷顿蛋白羧基端存在一个明确的、经典的出核信号,而新近的报道指出该蛋白的氨基端也存在一个胞浆定位相关功能域.通过对亨廷顿蛋白氨基端的部分氨基酸缺失和点突变等方式来研究该功能域,继而用免疫荧光和Western等技术观察该蛋白表达、聚集物形成和细胞内定位.结果发现,4~17个氨基酸是亨廷顿蛋白胞浆定位所必需的.L4R和L7R(由疏水氨基酸变为亲水氨基酸)的突变方式会导致1~17个氨基酸胞浆定位功能的缺失,而L4M和M8L(均为疏水氨基酸)的突变方式并未影响1~17个氨基酸的胞浆定位功能,说明其胞浆定位功能的维系依赖于该段序列的空间结构.前3个氨基酸的缺失并未影响前17个氨基酸与线粒体的共定位.同时观察到,该胞浆定位序列的功能缺失将导致异常增多的CAG重复所致的聚集物总量减少、定位于核内的比例增高,表明亨廷顿蛋白在细胞内的分布一定程度上也影响了聚集物的形成过程.这些结果对进一步研究聚集物的分子机制有一定的启示作用.

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