title: Systemic RNA Interference Deficiency-1 (SID-1) Extracellular Domain Selectively Binds Long Double-stranded RNA and Is Required for RNA Transport by SID-1.
abstract: During systemic RNA interference (RNAi) in Caenorhabditis elegans, RNA spreads across different cells and tissues in a process that requires the systemic RNA interference deficient-1 (sid-1) gene, which encodes an integral membrane protein. SID-1 acts cell-autonomously and is required for cellular import of interfering RNAs. Heterologous expression of SID-1 in Drosophila Schneider 2 cells enables passive uptake of dsRNA and subsequent soaking RNAi. Previous studies have suggested that SID-1 may serve as an RNA channel, but its precise molecular role remains unclear. To test the hypothesis that SID-1 mediates a direct biochemical recognition of RNA molecule and subsequent permeation, we expressed the extracellular domain (ECD) of SID-1 and purified it to near homogeneity. Recombinant purified SID-1 ECD selectively binds dsRNA but not dsDNA in a length-dependent and sequence-independent manner. Genetic missense mutations in SID-1 ECD causal for deficient systemic RNAi resulted in significant reduction in its affinity for dsRNA. Furthermore, full-length proteins with these mutations decrease SID-1-mediated RNA transport efficiency, providing evidence that dsRNA binding to SID-1 ECD is related to RNA transport. To examine the functional similarity of mammalian homologs of SID-1 (SIDT1 and SIDT2), we expressed and purified mouse SIDT1 and SIDT2 ECDs. We show that they bind long dsRNA in vitro, supportive of dsRNA recognition. In summary, our study illustrates the functional importance of SID-1 ECD as a dsRNA binding domain that contributes to RNA transport.
authors.affiliation: From the Solomon H. Snyder Department of Neuroscience, the Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Li
authors.affiliation: the Department of Molecular Biology and Genetics, and.
authors.forename: Kristin S
authors.initials: KS
authors.lastname: Koutmou
authors.affiliation: the Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Leahy
authors.affiliation: From the Solomon H. Snyder Department of Neuroscience, GlaxoSmithKline, King of Prussia, Pennsylvania 19406 min.x.li@gsk.com.
authors.forename: Min
authors.initials: M
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034443:RNA Transport; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D008565:Membrane Proteins; D012330:RNA, Double-Stranded; C452203:SID-1 protein, C elegans; D004247:DNA
keywords: RNA; RNA interference (RNAi); RNA transport; RNA-binding protein; RNA-protein interaction; SID-1; SIDT1; SIDT2