Crystal structure of a PIWI protein suggests mechanisms for siRNA recognition and slicer activity
Crystal structure of a PIWI protein suggests mechanisms for siRNA recognition and slicer activity
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DOI：
10.1038/sj.emboj.7600488
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发表时间：
2004-12-08
期刊：
影响因子：
11.4
通讯作者：
Barford, D
中科院分区：
文献类型：
--
作者：
Parker, JS;Roe, SM;Barford, D
RNA沉默通过mRNA降解、翻译抑制和染色质重塑来调节基因表达。RNA沉默的基本引擎是RISC和RITS复合物，其共同组分是21-25 nt RNA和含有未知功能的PIWI结构域的Argonaute蛋白。古生菌Piwi蛋白（AfPiwi）的晶体结构被组织成两个结构域，一个类似于乳糖阻遏物的糖结合部分，另一个类似于RNA酶H。恒定残基和配位金属离子位于蛋白质保守C末端周围的口袋中，定义了PIWI结构域中的关键功能区。此外，在大多数Argonaute序列中保守的两个Asp残基与RNase H样催化位点的催化性Asp残基在空间上对齐，这表明在真核Argonaute蛋白中RNase H样结构域可能具有核酸酶活性。PIWI结构域的C末端周围的保守区域（其是小干扰RNA（siRNA）结合至AfPiwi所需的）可以充当siRNA的强制性50磷酸的受体位点，从而指定靶mRNA的切割位置。
RNA silencing regulates gene expression through mRNA degradation, translation repression and chromatin remodelling. The fundamental engines of RNA silencing are RISC and RITS complexes, whose common components are 21-25 nt RNA and an Argonaute protein containing a PIWI domain of unknown function. The crystal structure of an archaeal Piwi protein (AfPiwi) is organised into two domains, one resembling the sugar-binding portion of the lac repressor and another with similarity to RNase H. Invariant residues and a coordinated metal ion lie in a pocket that surrounds the conserved C-terminus of the protein, defining a key functional region in the PIWI domain. Furthermore, two Asp residues, conserved in the majority of Argonaute sequences, align spatially with the catalytic Asp residues of RNase H-like catalytic sites, suggesting that in eukaryotic Argonaute proteins the RNase H-like domain may possess nuclease activity. The conserved region around the C-terminus of the PIWI domain, which is required for small interfering RNA (siRNA) binding to AfPiwi, may function as the receptor site for the obligatory 50 phosphate of siRNAs, thereby specifying the cleavage position of the target mRNA.