Key catalytic enzyme of RNAi, has diverse reaction pathways on Target RNAs
By using single-molecule fluorescence measurements, in a recent contribution by the Song lab at KAIST have shown that the target binding of core-RISCm Argonaute2 starts at the seed region, resulting in four distinct reaction pathways: target cleavage, transient binding, stable binding, and Argonaute unloading. In particular, the stable binding of core-RISC provides a potential explanation for the seed-match rule of miRNA
Small-RNA mediated gene silencing mechanism is the key mechanism required to fine-tune gene expression. Despite the existence many structural and biochemical studies, the reaction pathway of Argonaute, the RNAi catalytic enzyme, has not been clearly understood. Here, using single-molecule fluorescence measurements, the researchers characterized the reaction mechanisms of the core-RISC (RNA-induced silencing complex) comprised of human Argonaute2 and a small RNA. We found that when the core-RISC binds to the target, the core-RISC and the target result in four distinct reaction pathways. First, the core-RISC simply cleaves the target. Second, the core-RISC transiently binds to the target and dissociates. Third, once Argonaute-small RNA binds to the target, Argonaute is unloaded from the small RNA-target complex. Lastly, but most interestingly, the core-RISC binds to the target and keeps stably resting at the target. This stable binding of core-RISC at the target provides a mechanistic explanation for the action mode of miRNA. Overall, this work helps dissect reaction pathways used by Argonaute, the catalytic enzyme of RNAi.
This work has been done in collaboration with Sungchul Hohng at Seoul National University.
REFERENCE: Myung Hyun Jo*, Soochul Shin*, Seung-Ryoung Jung, Eunji Kim, Ji-Joon Song, and Sungchul Hohng, “Human Argonaute 2 has diverse reaction pathways on target RNAs”, Molecular Cell, accepted *equal contribution