Poster abstracts
Poster number 58 submitted by Huaqun Zhang
Structural Basis for RISC Assembly of Human Argonaute2
Huaqun Zhang (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA.), Vishal Annasaheb Adhav, Audrey C. Kehling (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA.), Andrew Savidge (Ohio State Biochemistry Program and Center for RNA Biology, The Ohio State University, Columbus, Ohio, USA.), Zhangfei Shen, Tian-Min Fu (Ohio State Biochemistry Program, Center for RNA Biology, Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio, USA), Kotaro Nakanishi (Department of Chemistry and Biochemistry, Ohio State Biochemistry Program, Center for RNA Biology, and Molecular, Cellular and Developmental Biology, The Ohio State University, Columbus, Ohio, USA.)
Abstract:
Argonaute proteins (AGOs) load small RNA duplexes and select one strand to form the RNA-induced silencing complex (RISC), but the mechanism of assembly remains unclear. We report four cryogenic-electron microscopy structures of human AGO2 bound to an siRNA duplex, capturing previously unanticipated intermediates. Unexpectedly, only the MID–PIWI lobe secures one duplex end, while α-helix 14 probes its stability. When the N domain reaches the opposite end, the L1 hairpin and Stalk wedge into the duplex and the PAZ domain engages the guide 3′ end. This configuration peels the passenger from its 5′ end while leaving it paired to the guide seed. AGO2 completely ejects the passenger by replacing it even with partially complementary target RNAs. This target-assisted passenger ejection (TAPE) also operates for the cleaved passenger strand. Our study uncovers that mRNAs are bifunctional molecules that not only serve as targets of RISCs but also help drive RISC assembly.
Keywords: Argonaute, RNA-induced silencing complex, RISC assembly