Bacterial Riboswitches and Ribozymes Potently Activate the Human Innate Immune Sensor PKR.
Bacterial Riboswitches and Ribozymes Potently Activate the Human Innate Immune Sensor PKR.
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DOI：
10.1021/acschembio.6b00081
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发表时间：
2016-04-15
影响因子：
4
通讯作者：
Bevilacqua PC
中科院分区：
文献类型：
--
作者：
Hull CM;Anmangandla A;Bevilacqua PC
先天免疫系统通过识别RNA中的非特异性模式来提供针对病原体的第一道防线，以广义的方式保护细胞。人RNA活化蛋白激酶PKR是一种dsRNA结合蛋白，是先天免疫应答中的重要传感器，通过RNA识别病毒和细菌病原体。通过RNA依赖性自磷酸化激活后，PKR磷酸化真核起始因子eIF 2 α，导致翻译终止。PKR在识别病毒RNA中具有良好的特征化作用，其中它非序列特异性地结合长链双链RNA以促进激活;然而，细菌RNA激活PKR的机制和自身RNA避免激活PKR的模式尚不清楚。我们的特点是激活PKR的三个功能性细菌RNA与假结和广泛的三级结构：环二GMP核糖开关，glmS核糖开关核酶，和扭转核酶，其中两个是配体激活。发现这些RNA以与长dsRNA相当的效力激活PKR。在PKR存在和不存在的情况下的酶结构图谱揭示了清晰的PKR足迹，并为这些细菌RNA如何激活PKR提供了结构基础。在环状二GMP核糖开关和glmS核糖开关-核酶的情况下，PKR似乎在天然RNA三级结构的外周双链区域上二聚化。总的来说，这些结果提供了新的见解PKR如何作为一种先天免疫信号蛋白的存在细菌，并提出了一个明显缺乏蛋白质的核糖开关和核酶在人类基因组中的原因。
The innate immune system provides the first line of defense against pathogens through the recognition of non-specific patterns in RNA to protect the cell in a generalized way. The human RNA-activated protein kinase, PKR, is a dsRNA binding protein and an essential sensor in the innate immune response, which recognizes viral and bacterial pathogens through their RNAs. Upon activation via RNA-dependent autophosphorylation, PKR phosphorylates the eukaryotic initiation factor eIF2α leading to termination of translation. PKR has a well-characterized role in recognizing viral RNA, where it binds long stretches of double-stranded RNA non-sequence specifically to promote activation; however, the mechanism by which bacterial RNA activates PKR and the mode by which self RNA avoids activating PKR are unknown. We characterized activation of PKR by three functional bacterial RNAs with pseudoknots and extensive tertiary structure: the cyclic-di GMP riboswitch, the glmS riboswitch-ribozyme, and the twister ribozyme, two of which are ligand-activated. These RNAs were found to activate PKR with comparable potency to long dsRNA. Enzymatic structure mapping in the absence and presence of PKR reveals a clear PKR footprint and provides a structural basis for how these bacterial RNAs activate PKR. In the case of the cyclic di-GMP riboswitch and the glmS riboswitch-ribozyme, PKR appears to dimerize on the peripheral double-stranded regions of the native RNA tertiary structure. Overall, these results provide new insights into how PKR acts as an innate immune signaling protein for the presence of bacteria and suggest a reason for the apparent absence of protein-free riboswitches and ribozymes in the human genome.