Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
Genes Dev. 2011 May 1;25(9):917-29. doi: 10.1101/gad.623011.
Removal of the assembly factor eukaryotic initiation factor 6 (eIF6) is critical for late cytoplasmic maturation of 60S ribosomal subunits. In mammalian cells, the current model posits that eIF6 release is triggered following phosphorylation of Ser 235 by activated protein kinase C. In contrast, genetic studies in yeast indicate a requirement for the ortholog of the SBDS (Shwachman-Bodian-Diamond syndrome) gene that is mutated in the inherited leukemia predisposition disorder Shwachman-Diamond syndrome (SDS). Here, by isolating late cytoplasmic 60S ribosomal subunits from Sbds-deleted mice, we show that SBDS and the GTPase elongation factor-like 1 (EFL1) directly catalyze eIF6 removal in mammalian cells by a mechanism that requires GTP binding and hydrolysis by EFL1 but not phosphorylation of eIF6 Ser 235. Functional analysis of disease-associated missense variants reveals that the essential role of SBDS is to tightly couple GTP hydrolysis by EFL1 on the ribosome to eIF6 release. Furthermore, complementary NMR spectroscopic studies suggest unanticipated mechanistic parallels between this late step in 60S maturation and aspects of bacterial ribosome disassembly. Our findings establish a direct role for SBDS and EFL1 in catalyzing the translational activation of ribosomes in all eukaryotes, and define SDS as a ribosomopathy caused by uncoupling GTP hydrolysis from eIF6 release.
去除组装因子真核起始因子 6（eIF6）对于 60S 核糖体亚基的晚期细胞质成熟至关重要。在哺乳动物细胞中，目前的模型假设 eIF6 的释放是在蛋白激酶 C 激活后 Ser235 磷酸化触发的。相比之下，酵母的遗传研究表明需要 SBDS（Shwachman-Bodian-Diamond 综合征）基因的同源物，该基因在遗传性白血病易感性疾病 Shwachman-Diamond 综合征（SDS）中发生突变。在这里，我们通过从小鼠中分离晚期细胞质 60S 核糖体亚基，表明 SBDS 和 GTP 延伸因子样 1（EFL1）直接通过需要 EFL1 的 GTP 结合和水解但不需要 eIF6 Ser235 磷酸化的机制在哺乳动物细胞中催化 eIF6 的去除。对与疾病相关的错义变体的功能分析表明，SBDS 的主要作用是将 EFL1 在核糖体上的 GTP 水解紧密偶联到 eIF6 的释放。此外，互补的 NMR 光谱研究表明，60S 成熟的这一晚期步骤与细菌核糖体解体的某些方面之间存在出人意料的机制相似性。我们的研究结果确立了 SBDS 和 EFL1 在催化所有真核生物核糖体翻译激活中的直接作用，并将 SDS 定义为一种由于 eIF6 释放与 GTP 水解解偶联而导致的核糖体病。
