Structural basis for RNA slicing by a plant Argonaute

Area of Science:

• Molecular Biology
• Structural Biology
• Plant Science

Background:

• Argonaute (AGO) proteins are crucial for gene silencing in eukaryotes and prokaryotes.
• Eukaryotic AGOs utilize small RNAs to target complementary transcripts for cleavage (slicing).
• Structural understanding of RNA-guided slicing by eukaryotic AGOs remains limited.

Purpose of the Study:

• To elucidate the structural mechanisms of RNA-guided slicing by eukaryotic Argonaute proteins.
• To compare the slicing mechanisms of eukaryotic AGOs with those of prokaryotic AGOs.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) was used to determine the structures of Arabidopsis thaliana Argonaute10 (AtAgo10).
• Structures were obtained for the AtAgo10-guide RNA complex with and without a target RNA substrate.
• Analysis of protein-RNA interactions and conformational changes associated with slicing competency.

Main Results:

• The AtAgo10-guide-target complex adopts unique slicing-competent and -incompetent conformations distinct from prokaryotic AGOs.
• Target RNA nucleotides (t9-t13) docking into a surface channel licenses AtAgo10 slicing activity.
• A β-hairpin in the L1 domain plays a key role in securing the target RNA and coordinating docking with guide-target pairing.

Conclusions:

• Prokaryotic and eukaryotic AGOs employ divergent mechanisms for target RNA slicing.
• Structural insights into AtAgo10 provide a framework for understanding small interfering RNA potency and gene regulation in plants.