Structure of RDE-4 dsRBDs and mutational studies provide insights in the dsRNA recognition in C. elegans RNAi pathway

The association of RDE-4, a protein containing two double stranded RNA binding domains (dsRBDs), with long dsRNA and Dicer (Dcr-1) initiates the siRNA pathway in C. elegans. Unlike its homologs in higher eukaryotes, RDE-4 dsRBDs possess weak (micromolar) affinity for short dsRNA. With the increasing length of dsRNA, RDE-4 exhibits enhanced affinity due to cooperativity. The linker and dsRBD2 are indispensable for RDE-4’s simultaneous interaction with dsRNA and Dcr-1. Here, we present the solution structures of RDE-4 constructs that contain both dsRBDs and the linker region. In addition to the canonical dsRBD fold, both dsRBDs of RDE-4 show modified structural features such as truncation in the β1-β2 loop that rationalize RDE-4’s relatively weak dsRNA affinity. Structure and binding studies demonstrate that dsRBD2 plays a decisive role in RDE-4:dsRNA interaction, however, contrary to previous findings, we report ephemeral interaction of RDE-4 dsRBD1 with dsRNA. More importantly, mutations in two tandem lysine residues (K217 and K218) in dsRBD2 impair RDE-4’s dsRNA binding ability and could obliterate RNAi initiation in C. elegans. Additionally, our studies postulate a structural basis for the minimal requirement of linker and dsRBD2 for RDE-4’s association with dsRNA and Dcr-1.

Source: BJ Gene - November 21, 2013 Category: Biochemistry Authors: S Chiliveri, M V. Deshmukh Tags: BJ Biomolecules Source Type: research