Poster abstracts
Poster number 101 submitted by Hong-Duc Phan
Structural and functional characterization of human Argonaute4
Hong-Duc Phan (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, 43210), Miseul Park (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, 43210), James A. Brackbill (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, 43210), Kotaro Nakanishi (Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, 43210)
Abstract:
Human Argonaute4 (AGO4) is a slicer-independent Argonaute protein that uses the loaded microRNA to bind to target mRNAs and triggers translational repression and deadenylation. Recent studies reported that AGO4 plays specialized roles in regulating spermatogenesis and internal ribosome entry site-driven translation although those molecular mechanisms remain unknown. To understand how AGO4 treats the bound miRNA differently from other paralogues, we determined the crystal structure of AGO4 in the complex with guide RNA at 1.9 Å. Unlike the previously reported model, our structure showed that a different glutamate was rearranged to complete the pseudo catalytic tetrad. The consensus of the rearrangement with other paralogues imply another role of the corresponding glutamate in addition to the catalytic reaction. An AGO4-specific insertion loop, previously proposed to be poised on the PIWI domain, actually protruded towards the nucleic acid-binding channel. Our target-strand docking model suggested that the loop interfered with the propagation of guide-target duplex. In contrast, AGO2 possessed a kink-turn at the corresponding position and did not seem to interact with the duplex. Supporting this, an implant of the AGO4-specific insertion loop into AGO2 completely disrupted the target cleavage. These data demonstrate that the specific loop confers a different target specificity on AGO4.
Keywords: AGO4, crystal structure, insertion loop