title: Structure of the carboxy-terminal receptor-binding domain of avian reovirus fibre sigmaC.
abstract: Avian reovirus fibre, a homo-trimer of the sigmaC protein, is responsible for primary host cell attachment. The protein expressed in bacteria forms elongated fibres comprised of a carboxy-terminal globular head domain and a slender shaft, and partial proteolysis yielded a carboxy-terminal protease-stable domain that was amenable to crystallisation. Here, we show that this fragment retains receptor-binding capability and report its structure, solved using two-wavelength anomalous diffraction and refined using data collected from three different crystal forms at 2.1 angstroms, 2.35 angstroms and 3.0 angstroms resolution. The carboxy-terminal globular domain has a beta-barrel fold with the same overall topology as the mammalian reovirus fibre (sigma1). However, the monomers of the sigmaC trimer show a more splayed-out arrangement than in the sigma1 structure. Also resolved are two triple beta-spiral repeats of the shaft or stalk domain. The presence in the sequence of heptad repeats amino-terminal to these triple beta-spiral repeats suggests that the unresolved portion of the shaft domain contains a triple alpha-helical coiled-coil structure. Implications for the function and stability of the sigmaC protein are discussed.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Santiago de Compostela, Campus Sur, E-15782 Santiago de Compostela, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Guardado Calvo
authors.forename: Gavin C
authors.initials: GC
authors.lastname: Fox
authors.forename: X Lois
authors.initials: XL
authors.lastname: Hermo Parrado
authors.forename: Antonio L
authors.initials: AL
authors.lastname: Llamas-Saiz
authors.forename: Celina
authors.initials: C
authors.lastname: Costas
authors.forename: José
authors.initials: J
authors.lastname: Martínez-Costas
authors.forename: Javier
authors.initials: J
authors.lastname: Benavente
authors.forename: Mark J
authors.initials: MJ
authors.lastname: van Raaij
mesh_terms: D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D030101:Orthoreovirus, Avian / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011991:Receptors, Virus / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D036022:Capsid Proteins; D011991:Receptors, Virus; C031728:sigma 1 protein, reovirus