Structure of the carboxy-terminal receptor-binding domain of avian reovirus fibre sigmaC.
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.
Guardado Calvo
Pablo
P
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Santiago de Compostela, Campus Sur, E-15782 Santiago de Compostela, Spain.
Fox
Gavin C
GC
Hermo Parrado
X Lois
XL
Llamas-Saiz
Antonio L
AL
Costas
Celina
C
Martínez-Costas
José
J
Benavente
Javier
J
van Raaij
Mark J
MJ
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
D036022:Capsid Proteins; D011991:Receptors, Virus; C031728:sigma 1 protein, reovirus