RESUMO
Infectious bursal disease virus (IBDV), a member of the Birnaviridae group, is a commercially important pathogen of chickens. From electron micrographs of frozen, hydrated, unstained specimens, we have computed a three-dimensional map of IBDV at about 2 nm resolution. The map shows that the structure of the virus is based on a T=13 lattice and that the subunits are predominantly trimer clustered. The subunits close to the fivefold symmetry axes are at a larger radius than those close to the two- or threefold axes, giving the capsid a markedly nonspherical shape. The trimer units on the outer surface protrude from a continuous shell of density. On the inner surface, the trimers appear as Y-shaped units, but the set of units surrounding the fivefold axes appears to be missing. It is likely that the outer trimers correspond to the protein VP2, carrying the dominant neutralizing epitope, and the inner trimers correspond to protein VP3, which has a basic carboxy-terminal tail expected to interact with the packaged RNA.
Assuntos
Vírus da Doença Infecciosa da Bursa/ultraestrutura , Microscopia Eletrônica/métodos , Animais , Capsídeo/ultraestrutura , Galinhas/virologia , Criopreservação , Processamento de Imagem Assistida por ComputadorRESUMO
Small crystals of leucine aminopeptidase were prepared in 2 percent ammonium molybdate. Single molecules were contrasted with 2 percent potassium silico tungstate which gave better contrast and preservation of enzyme activity than ammonium molybdate. The six subunits of the enzyme consist of a spheroidal "head" and some "tail-like" material, which connects the "heads" in pairs. The subunits are arranged at the vertices of either a right triangular prism or of an oblique prism twisted by 42 degree (symmetry 32).