In miRNA-mediated gene silencing, the physical interaction between human Argonaute (hAgo) and GW182 (hGW182) is essential for facilitating the downstream silencing of the targeted mRNA. GW182 can interact with hAgo via three of the GW/WG repeats in its Argonaute-binding domain: motif-1, motif-2, and the hook motif. The structure of hAgo1 in complex with the hook motif of hGW182 reveals a “gate”-like interaction that is critical for GW182 docking into one of hAgo1’s tryptophan-binding pockets. We show that hAgo1 and hAgo2 have a single GW182-binding site and that miRNA binding increases hAgo’s affinity to GW182. With target binding occurring rapidly, this ensures that only mature RISC would be recruited for silencing. Finally, we show that hGW182 can recruit up to three copies of hAgo via its three GW motifs. This may explain the observed cooperativity in miRNA-mediated gene silencing.

在 miRNA 介导的基因沉默中，人类 Argonaute (hAgo) 和 GW182 (hGW182) 之间的物理相互作用对于促进靶向 mRNA 的下游沉默至关重要。GW182 可以通过其 Argonaute 结合域中的三个 GW/WG 重复序列与 hAgo 相互作用：motif-1、motif-2 和 hook motif。hAgo1 的结构与 hGW182 的钩基序复合，揭示了一种类似“门”的相互作用，这对于 GW182 与 hAgo1 的色氨酸结合口袋之一的对接至关重要。我们表明 hAgo1 和 hAgo2 具有单个 GW182 结合位点，并且 miRNA 结合增加了 hAgo 对 GW182 的亲和力。随着目标绑定迅速发生，这确保了只有成熟的 RISC 才会被招募用于沉默。最后，我们表明 hGW182 可以通过其三个 GW 基序招募多达三个 hAgo 副本。