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腾讯登录Nature: RNA干扰复合物的晶体结构
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已知Argonaute蛋白是一种结合RNA的蛋白质，研究人员已经鉴定并分析了酵母Argonaute蛋白的晶体结构。在沉默基因的RNA干扰（RNAi）通路中，这种Argonaute-RNA复合物起着关键作用，描述真核生物Argonaute蛋白分子结构一直是RNA干扰领域近十年的目标。了解Argonaute晶体结构不仅是理解RNAi生化通路很重要的一步，也是将来许多实验的依据。
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在人和其他真核生物中，RNAi通路能通过减少蛋白质的RNA模板来降低细胞内蛋白生产。利用这条通路，科学家能敲除特定蛋白的表达，从而测定它们在细胞或组织中的作用；在人类疾病的治疗方面，RNAi通路也相当重要。
RNAi依赖两种蛋白，即Dicer 和Argonaute，其中Dicer识别双链RNA（dsRNA），锁定在dsRNA上，并将其切成21-23个核苷酸长的碎片；Argonaute识别上述的dsRNA碎片，清除双链RNA中一条链，用另一条链作为向导RNA，当单链RNA匹配上向导RNA序列时，Argonaute即裂解此单链RNA，从而防止它作为蛋白生产的模板。
为了测定Argonaute结构，研究人员通力合作，希望能解决Argonaute结构问题，结果发现它是一个具有复杂拓扑结构和许多活动部分的大蛋白，确实是一个令人印象深刻的分子机器，在结构中伴有少量RNA，这些RNA的掺入将Argonaute蛋白转变成一种含4元件活化部位的激活态。这样，一个长期以来的谜，即什么构成了"消失的"第四元件，也就得到了解答。有这个结构在手，科学家现在就能更好地了解它怎么运作。
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<img src="http://www.bioon.com/biology/UploadFiles/201206/2012062110451989.jpg" alt="" width="113" height="149" border="0" hspace="0" />
<a title="" href="http://dx.doi.org/10.1038/nature11211" target="_blank">doi:10.1038/nature11211</a>
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<br/><strong>Structure of yeast Argonaute with guide RNA</strong><br/>
Kotaro Nakanishi, David E. Weinberg, David P. Bartel, Dinshaw J. Patel
The RNA-induced silencing complex, comprising Argonaute and guide RNA, mediates RNA interference. Here we report the 3.2?? crystal structure ofKluyveromyces polysporus Argonaute (KpAGO) fortuitously complexed with guide RNA originating from small-RNA duplexes autonomously loaded by recombinant KpAGO. Despite their diverse sequences, guide-RNA nucleotides 1-8 are positioned similarly, with sequence-independent contacts to bases, phosphates and 2′-hydroxyl groups pre-organizing the backbone of nucleotides 2-8 in a near-A-form conformation. Compared with prokaryotic Argonautes, KpAGO has numerous surface-exposed insertion segments, with a cluster of conserved insertions repositioning the N domain to enable full propagation of guide-target pairing. Compared with Argonautes in inactive conformations, KpAGO has a hydrogen-bond network that stabilizes an expanded and repositioned loop, which inserts an invariant glutamate into the catalytic pocket. Mutation analyses and analogies to ribonuclease H indicate that insertion of this glutamate finger completes a universally conserved catalytic tetrad, thereby activating Argonaute for RNA cleavage.
<br/>来源：生物谷
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已知Argonaute蛋白是一种结合RNA的蛋白质，研究人员已经鉴定并分析了酵母Argonaute蛋白的晶体结构。在沉默基因的RNA干扰（RNAi）通路中，这种Argonaute-RNA复合物起着关键作用，描述真核生物Argonaute蛋白分子结构一直是RNA干扰领域近十年的目标。了解Argonaute晶体结构不仅是理解RNAi生化通路很重要的一步，也是将来许多实验的依据。
<!--more-->
在人和其他真核生物中，RNAi通路能通过减少蛋白质的RNA模板来降低细胞内蛋白生产。利用这条通路，科学家能敲除特定蛋白的表达，从而测定它们在细胞或组织中的作用；在人类疾病的治疗方面，RNAi通路也相当重要。
RNAi依赖两种蛋白，即Dicer 和Argonaute，其中Dicer识别双链RNA（dsRNA），锁定在dsRNA上，并将其切成21-23个核苷酸长的碎片；Argonaute识别上述的dsRNA碎片，清除双链RNA中一条链，用另一条链作为向导RNA，当单链RNA匹配上向导RNA序列时，Argonaute即裂解此单链RNA，从而防止它作为蛋白生产的模板。
为了测定Argonaute结构，研究人员通力合作，希望能解决Argonaute结构问题，结果发现它是一个具有复杂拓扑结构和许多活动部分的大蛋白，确实是一个令人印象深刻的分子机器，在结构中伴有少量RNA，这些RNA的掺入将Argonaute蛋白转变成一种含4元件活化部位的激活态。这样，一个长期以来的谜，即什么构成了"消失的"第四元件，也就得到了解答。有这个结构在手，科学家现在就能更好地了解它怎么运作。
<div id="ztload">
<div>
<div>
<img src="http://www.bioon.com/biology/UploadFiles/201206/2012062110451989.jpg" alt="" width="113" height="149" border="0" hspace="0" />
<a title="" href="http://dx.doi.org/10.1038/nature11211" target="_blank">doi:10.1038/nature11211</a>
PMC:
PMID:
</div>
<div>
<br/><strong>Structure of yeast Argonaute with guide RNA</strong><br/>
Kotaro Nakanishi, David E. Weinberg, David P. Bartel, Dinshaw J. Patel
The RNA-induced silencing complex, comprising Argonaute and guide RNA, mediates RNA interference. Here we report the 3.2?? crystal structure ofKluyveromyces polysporus Argonaute (KpAGO) fortuitously complexed with guide RNA originating from small-RNA duplexes autonomously loaded by recombinant KpAGO. Despite their diverse sequences, guide-RNA nucleotides 1-8 are positioned similarly, with sequence-independent contacts to bases, phosphates and 2′-hydroxyl groups pre-organizing the backbone of nucleotides 2-8 in a near-A-form conformation. Compared with prokaryotic Argonautes, KpAGO has numerous surface-exposed insertion segments, with a cluster of conserved insertions repositioning the N domain to enable full propagation of guide-target pairing. Compared with Argonautes in inactive conformations, KpAGO has a hydrogen-bond network that stabilizes an expanded and repositioned loop, which inserts an invariant glutamate into the catalytic pocket. Mutation analyses and analogies to ribonuclease H indicate that insertion of this glutamate finger completes a universally conserved catalytic tetrad, thereby activating Argonaute for RNA cleavage.
<br/>来源：生物谷
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