title: Purification and crystallization reveal two types of interactions of the fusion protein homotrimer of Semliki Forest virus.
abstract: The fusion proteins of the alphaviruses and flaviviruses have a similar native structure and convert to a highly stable homotrimer conformation during the fusion of the viral and target membranes. The properties of the alpha- and flavivirus fusion proteins distinguish them from the class I viral fusion proteins, such as influenza virus hemagglutinin, and establish them as the first members of the class II fusion proteins. Understanding how this new class carries out membrane fusion will require analysis of the structural basis for both the interaction of the protein subunits within the homotrimer and their interaction with the viral and target membranes. To this end we report a purification method for the E1 ectodomain homotrimer from the alphavirus Semliki Forest virus. The purified protein is trimeric, detergent soluble, retains the characteristic stability of the starting homotrimer, and is free of lipid and other contaminants. In contrast to the postfusion structures that have been determined for the class I proteins, the E1 homotrimer contains the fusion peptide region responsible for interaction with target membranes. This E1 trimer preparation is an excellent candidate for structural studies of the class II viral fusion proteins, and we report conditions that generate three-dimensional crystals suitable for analysis by X-ray diffraction. Determination of the structure will provide our first high-resolution views of both the low-pH-induced trimeric conformation and the target membrane-interacting region of the alphavirus fusion protein.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Don L
authors.initials: DL
authors.lastname: Gibbons
authors.forename: Brigid
authors.initials: B
authors.lastname: Reilly
authors.forename: Anna
authors.initials: A
authors.lastname: Ahn
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Vaney
authors.forename: Armelle
authors.initials: A
authors.lastname: Vigouroux
authors.forename: Felix A
authors.initials: FA
authors.lastname: Rey
authors.forename: Margaret
authors.initials: M
authors.lastname: Kielian
mesh_terms: D000818:Animals; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D006224:Cricetinae; D003460:Crystallization; D018360:Crystallography, X-Ray; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008027:Light; D008081:Liposomes; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012542:Scattering, Radiation; D012672:Semliki forest virus / Q000737:chemistry*; D012995:Solubility; D014760:Viral Fusion Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D008081:Liposomes; D014760:Viral Fusion Proteins