The structural basis for RNA slicing by human Argonaute2

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Argonaute (AGO) proteins are central to RNA interference (RNAi), a fundamental gene silencing process in eukaryotes.
• RNAi is crucial for cellular function and is the basis for novel clinical therapies.
• Structural data for AGOs in a fully paired, slicing-competent state, crucial for RNAi, has been limited due to its hypothesized instability.

Purpose of the Study:

• To determine the structure of a human AGO-guide complex bound to a fully paired target RNA.
• To elucidate the structural rearrangements enabling this slicing-competent conformation.
• To understand how AGO proteins achieve high specificity and efficiency in target RNA recognition and slicing.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) was used to determine the high-resolution structure.
• The study focused on a human AGO-guide complex interacting with a perfectly complementary target RNA molecule.

Main Results:

• The structure reveals significant rearrangements within the AGO protein, particularly the N domain, facilitating target RNA binding in the central channel.
• A conserved loop in the PIWI domain was identified, which stabilizes the target RNA near the active site, enhancing slicing efficiency and specificity.
• These structural adaptations explain AGO's ability to process targets with the precise base-pairing typically seen in biological and clinical contexts.

Conclusions:

• The study provides the first structural evidence of a human AGO-guide complex in a fully paired, slicing-competent conformation.
• The identified structural mechanisms, including N domain rotation and PIWI loop interaction, are key to AGO's function in RNAi.
• This work deepens our understanding of RNAi pathways and informs the development of RNA-based therapeutics.