New insights into the helicase domain of human Dicer and its biochemical properties: ATPase and RNA rearrangement activities
Vertebrates have one Dicer ortholog that generates both microRNAs (miRNAs) and small interfering RNAs (siRNAs), in contrast to the multiple Dicer-like proteins found in flies and plants. Here, we focus on the functions of the human Dicer (hDicer) helicase domain. The helicase domain of hDicer is known to recognize pre-miRNA substrates through interactions with their apical loop regions. Besides interacting with canonical substrates, the hDicer helicase domain has also been suggested to bind many different cellular RNAs; however, a comprehensive study of the biochemical activities and substrate specificity of the hDicer helicase domain towards different nucleic acids has yet to be undertaken. Here, we conduct such an analysis and reveal that full-length hDicer, through its helicase domain, hydrolyzes ATP. We also show that the hDicer helicase domain binds single-but not double-stranded RNAs and DNAs and that a structural rearrangement of the substrate accompanies the binding of single-stranded RNAs. This RNA rearrangement activity is ATP-independent. Our findings open new avenues for future studies aimed at defining the cellular activities of hDicer that may be associated with these newly described biochemical properties.