Structural insights into dsRNA processing by Drosophila Dicer-2/Loqs-PD

ABSTRACT: Small interfering RNAs (siRNAs) are the key components for RNA interference (RNAi), a conserved RNA silencing mechanism in many eukaryotes. In Drosophila, an RNase III enzyme Dicer-2 (Dcr-2), aided by its cofactor Loquacious-PD (Loqs-PD), plays major role in generating 21 base-pair (bp) siRNA duplexes from long double-stranded RNAs (dsRNAs). The ATP hydrolysis by the helicase domain of Dcr-2 is critical to the successful processing of a long dsRNA into consecutive siRNA duplexes. Here we report the cryo-EM structures of Dcr-2/Loqs-PD in the apo state and in multiple processing states of a 50-bp dsRNA substrate. The structures elucidated interactions between Dcr-2 and Loqs-PD, and significant conformational changes of Dcr-2 during a dsRNA processing cycle. The N-terminal helicase and DUF283 domains undergo conformational change upon initial dsRNA binding, forming an ATP binding pocket and a 5’-phosphate binding pocket. The overall conformation of Dcr-2/Loqs-PD is relatively rigid during translocating along the dsRNA in the presence of ATP, while the interaction between DUF283 and RIIIDb domains prevents non-specific cleavage during translocation by blocking the access of dsRNA to the RNase active center. Additional ATP-dependent conformational changes are required to form an active-dicing state and precisely cleave the dsRNA into 21-bp siRNA duplex confirmed by the structure in the post-dicing state. Collectively, this study revealed the molecular mechanism for the full-cycle of ATP-dependent dsRNA processing by Dcr-2/Loqs-PD.

ORGANISM(S): Drosophila Melanogaster

SUBMITTER: Jinbiao Ma  

PROVIDER: PXD033365 | iProX | Thu Apr 21 00:00:00 BST 2022

REPOSITORIES: iProX