Institute of Microbiology, University of Regensburg, 93053 Regensburg, Germany.
Center for Integrated Protein Science Munich CIPSM, Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
Nat Microbiol. 2017 Mar 20;2:17035. doi: 10.1038/nmicrobiol.2017.35.
Argonaute (Ago) proteins in eukaryotes are known as key players in post-transcriptional gene silencing, while recent studies on prokaryotic Agos hint at their role in the protection against invading DNA. Here, we present crystal structures of the apo enzyme and a binary Ago-guide complex of the archaeal Methanocaldococcus jannaschii (Mj) Ago. Binding of a guide DNA leads to large structural rearrangements. This includes the structural transformation of a hinge region containing a switch helix, which has been shown for human Ago2 to be critical for the dynamic target search process. To identify key residues crucial for MjAgo function, we analysed the effect of several MjAgo mutants. We observe that the nature of the 3' and 5' nucleotides in particular, as well as the switch helix, appear to impact MjAgo cleavage activity. In summary, we provide insights into the molecular mechanisms that drive DNA-guided DNA silencing by an archaeal Ago.
真核生物中的 Argonaute（AGO）蛋白被认为是转录后基因沉默的关键因子，而最近对原核 AGO 的研究表明它们在抵御入侵 DNA 方面发挥作用。在这里，我们展示了古菌 Methanocaldococcus jannaschii（Mj）AGO 的apo 酶和二元 Ago-向导复合物的晶体结构。向导 DNA 的结合导致了大的结构重排。这包括包含开关螺旋的铰链区域的结构转换，已经证明对于人类 Ago2 来说，这对于动态靶标搜索过程至关重要。为了鉴定对 MjAgo 功能至关重要的关键残基，我们分析了几个 MjAgo 突变体的影响。我们观察到，特别是 3'和 5'核苷酸的性质以及开关螺旋似乎影响 MjAgo 切割活性。总之，我们提供了有关驱动古菌 Ago 进行 DNA 引导的 DNA 沉默的分子机制的见解。
