Multidomain Convergence of Argonaute during RISC Assembly Correlates with the Formation of Internal Water Clusters

摘要: Despite the relevance of Argonaute proteins in RNA silencing, little is known about structural steps small loading to form RNA-induced silencing complexes (RISCs). We report 1.9 A crystal structure human Argonaute4 with guide RNA. Comparison previously determined apo Neurospora crassa QDE2 revealed that PIWI domain has two subdomains. Binding fastens subdomains, thereby rearranging active-site residues and increasing affinity for TNRC6 proteins. also identified water pockets beneath nucleic acid-binding channel appeared stabilize mature RISC. Indeed, mutating water-pocket Argonaute2 compromised RISC assembly. Simulations predict internal molecules are exchangeable bulk solvent but always occupy specific positions at interfaces. These results suggest after RNA-driven conformational changes, water-mediated hydrogen-bonding networks tie together converged domains complete functional structure.