The oligomeric architecture of the archaeal exosome is important for processive and efficient RNA degradation.
The oligomeric architecture of the archaeal exosome is important for processive and efficient RNA degradation.
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DOI：
10.1093/nar/gkw062
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发表时间：
2016-04-07
影响因子：
14.9
通讯作者：
Sprangers R
中科院分区：
文献类型：
--
作者：
Audin MJ;Wurm JP;Cvetkovic MA;Sprangers R
外泌体在RNA降解和加工中起着重要作用。在古细菌中，三个Rrp41:Rrp42异二聚体组装成一个桶状结构，其中包含一个狭窄的RNA入口孔和一个含有三个活性位点的管腔。在这里，我们证明了这种外泌体的四级结构对于有效的RNA降解是重要的。我们发现桶状材料的入口孔是纳米底物亲和力所必需的。这种强烈的相互作用对于底物降解至关重要，并防止RNA从酶中过早释放。使用甲基TROSY核磁共振技术，我们确定底物的3 '端在管腔内保持高度柔性。结果，RNA在三个活性位点之间跳跃，它们都平等地参与底物降解。然而，RNA跳跃速率远快于裂解速率，这表明并非所有的活性位点与底物相遇都会产生催化作用。因此，酶的周转得益于对管腔内活性位点和底物的限制，这确保了RNA始终与其中一个活性位点结合。因此，外泌体向六聚体复合物的进化及其催化效率的优化可能是共同发生的事件。
The exosome plays an important role in RNA degradation and processing. In archaea, three Rrp41:Rrp42 heterodimers assemble into a barrel like structure that contains a narrow RNA entrance pore and a lumen that contains three active sites. Here, we demonstrate that this quaternary structure of the exosome is important for efficient RNA degradation. We find that the entrance pore of the barrel is required for nM substrate affinity. This strong interaction is crucial for processive substrate degradation and prevents premature release of the RNA from the enzyme. Using methyl TROSY NMR techniques, we establish that the 3′ end of the substrate remains highly flexible inside the lumen. As a result, the RNA jumps between the three active sites that all equally participate in substrate degradation. The RNA jumping rate is, however, much faster than the cleavage rate, indicating that not all active site:substrate encounters result in catalysis. Enzymatic turnover therefore benefits from the confinement of the active sites and substrate in the lumen, which ensures that the RNA is at all times bound to one of the active sites. The evolution of the exosome into a hexameric complex and the optimization of its catalytic efficiency were thus likely co-occurring events.