Structural dynamics between Argonaute-2 and CK1α promote target RNA release in microRNA-mediated silencing.

Area of Science:

• Molecular Biology
• Structural Biology
• Gene Regulation

Background:

• Argonaute (Ago) proteins and microRNAs (miRNAs) form the RISC complex, crucial for post-transcriptional gene silencing.
• Target RNA binding to RISC triggers CK1α-mediated phosphorylation, releasing the target and enabling RISC reuse for efficient gene silencing.

Purpose of the Study:

• To elucidate the complete structural dynamics of human Ago2 during miRNA guide and target RNA binding.
• To visualize the conformational changes in RISC that facilitate CK1α binding and subsequent phosphorylation.

Main Methods:

• High-resolution structural analysis of human Ago2 complexed with guide-target RNA.
• Visualization of dynamic conformational changes in RISC during target engagement and phosphorylation.

Main Results:

• Ago2 binds guide-target RNA in an untwisted conformation, revealing the structural basis of miRNA-mediated gene silencing.
• Progressive base pairing between the guide and target RNA induces conformational changes, opening RISC to CK1α binding and initiating Ago2 phosphorylation.
• Complete supplementary pairing establishes a PAZ-CK1α interface, leading to hierarchical phosphorylation of the eukaryotic insertion (EI), which promotes RISC turnover.

Conclusions:

• The study provides a comprehensive structural understanding of how RISC facilitates miRNA-mediated gene silencing and efficient turnover.
• Phosphorylation of the EI domain, coupled with guide-target unwinding, is key to target RNA release and rapid RISC complex recycling.