The structure of human Argonaute-2 in complex with miR-20a

Argonaute proteins lie at the heart of the RNA-Induced Silencing Complex (RISC), wherein they use small RNA guides to recognize targets. Some Argonaute proteins can directly cleave their targets, whereas others recruit co-factors to repress independently of “slicing.” Prior studies established the architecture of Argonaute proteins; however, we have not yet had a detailed picture of an Argonaute whose biochemical and biological functions were well established. Here we describe the crystal structure of human Argonaute-2 bound to miR-20a at 2.2 A° resolution. Overall architecture and domain organization is shared with its prokaryotic counterparts, though Ago2 is somewhat more open, with its PAZ domain further removed from the other domains. The miRNA is anchored at both ends by the Mid and PAZ domains but makes several kinks and turns along the binding groove. The RNA confers remarkable stability on the Argonaute protein, locking this otherwise flexible enzyme into a stable conformation. Overall design: total small RNAs (19-29nt) and small RNAs associated with purified hArgonaute2 purified from SF9 cells. These were processed and sequenced on Illumina GA-II platform.