Characterization of the mammalian initiation factor eIF2B complex as a GDP dissociation stimulator protein
Characterization of the mammalian initiation factor eIF2B complex as a GDP dissociation stimulator protein
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DOI：
10.1074/jbc.m011788200
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发表时间：
2001-07-06
影响因子：
4.8
通讯作者：
Proud, CG
中科院分区：
文献类型：
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作者：
Williams, DD;Price, NT;Proud, CG
起始因子eIF 2B介导mRNA翻译起始的关键调节步骤，即活性eIF 2（.）GTP复合物。它由五个亚基组成，α-β。其中最大的（E）在没有其他的情况下显示出催化活性。eIF 2B的催化机制和其他亚基的功能仍有待阐明。在这里，我们表明，当存在于类似浓度的eIF 2，哺乳动物eIF 2B可以介导释放eIF 2结合的GDP，即使在没有游离核苷酸的情况下，这表明它作为GDP解离刺激蛋白。与此一致，向纯化的eIF 2（.）eIF 2B复合物使它们解离。替代的顺序机制将要求eIF 2B自身结合GTP。然而，我们发现是eIF 2B的β-亚基与GTP相互作用，这表明GTP与eIF 2B的结合不是其机制的必要因素。与全复合物相比，缺乏α-亚基的eIF 2B制剂显示出降低的活性。用重组eIF 2B α补充这些制剂显著增强活性，表明eIF 2B α是哺乳动物eIF 2B完全活性所必需的。
Initiation factor eIF2B mediates a key regulatory step in the initiation of mRNA translation, i.e. the regeneration of active eIF2(.)GTP complexes. It is composed of five subunits, alpha-epsilon. The largest of these (E) displays catalytic activity in the absence of the others. The catalytic mechanism of eIF2B and the functions of the other subunits remain to be clarified. Here we show that, when present at similar concentrations to eIF2, mammalian eIF2B can mediate release of eIF2-bound GDP even in the absence of free nucleotide, indicating that it acts as a GDP dissociation stimulator protein. Consistent with this, addition of GDP to purified eIF2(.)eIF2B complexes causes them to dissociate. The alternative sequential mechanism would require that eIF2B epsilon itself bind GTP. However, we show that it is the beta -subunit of eIF2B that interacts with GTP, This indicates that binding of GTP to eIF2B is not an essential element of its mechanism. eIF2B preparations that lack the alpha -subunit display reduced activity compared with the holocomplex. Supplementation of such preparations with recombinant eIF2B alpha markedly enhances activity, indicating that eIF2B alpha is required for full activity of mammalian eIF2B.