The Crystal Structure of Human Argonaute2

Human Argonaute Revealed RNA interference (RNAi) is mediated by Argonaute (Ago) proteins, which bind small regulatory RNAs that have sequence complementarity to target RNAs destined to be silenced. The structure of bacterial homologs of the Ago proteins, and fragments of eukaryotic Ago proteins, have provided initial insights into Ago function. Now, Schirle and MacRae (p. 1037 , published online 26 April; see the Perspective by Kaya and Doudna ) have determined the structure of the full-length human Ago protein bound to a single-stranded (ss) guide RNA. Within the bilobed structure, eight nucleotides of the ssRNA are visibly positioned in the RNA-guide, strand-binding site. The “seed” region of the ssRNA has its Watson-and-Crick base edges exposed to solvent, likely aiding target recognition. The location of two free tryptophans in the Piwi domain suggests a possible recruitment site for Ago-interacting proteins.