Preparation and characterization of the extracellular domain of human Sid-1

• Published in: PloS one Vol. 7; no. 4; p. e33607
• Main Authors: Pratt, Ashley J, Rambo, Robert P, Lau, Pick-Wei, MacRae, Ian J
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 11-04-2012; Public Library of Science (PLoS)
• Subjects: Access control; Animals; Baculoviridae - genetics; Baculovirus; BASIC BIOLOGICAL SCIENCES; Biology; Caenorhabditis elegans; Cell surface; Crystallography; Cytosol; Data analysis; Double-stranded RNA; Electron microscopy; Extracellular Space - metabolism; Gene expression; Genes; Glycosylation; Homology; Humans; Imports; Insects; Membrane Transport Proteins - chemistry; Membrane Transport Proteins - genetics; Membrane Transport Proteins - isolation & purification; Membrane Transport Proteins - metabolism; Models, Molecular; Molecular biology; Nematodes; Physiology; Potassium; Protein Folding; Protein Multimerization; Protein Processing, Post-Translational; protein structure; protein structure prediction; Protein Structure, Quaternary; Protein Structure, Tertiary; Proteins; Pyrococcus horikoshii; recombinant protein; Ribonucleic acid; RNA; RNA structure; RNA transport; RNA-mediated interference; Sequence Homology, Amino Acid; small angle scattering; Small angle X ray scattering; Solubility; Spodoptera - cytology; Trends; Vertebrates; Viral infections; X ray scattering; La Jolla California; United States > US; California
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0033607

In C. elegans, the cell surface protein Sid-1 imports extracellular dsRNA into the cytosol of most non-neuronal cells, enabling systemic spread of RNA interference (RNAi) throughout the worm. Sid-1 homologs are found in many other animals, although for most a function for the protein has not yet been established. Sid-1 proteins are composed of an N-terminal extracellular domain (ECD) followed by 9-12 predicted transmembrane regions. We developed a baculovirus system to express and purify the ECD of the human Sid-1 protein SidT1. Recombinant SidT1 ECD is glycosylated and spontaneously assembles into a stable and discrete tetrameric structure. Electron microscopy (EM) and small angle x-ray scattering (SAXS) studies reveal that the SidT1 ECD tetramer is a compact, puck-shaped globular particle, which we hypothesize may control access of dsRNA to the transmembrane pore. These characterizations provide inroads towards understanding the mechanism of this unique RNA transport system from structural prospective.