Adenovirus Structure by X-ray Crystallography and Electron Microscopy

Abstract

In the 40 years since the discovery of adenovirus, a wide range of biophysical and biochemical techniques have been applied to understanding the structure of the virion (Ginsberg 1979; Philipson 1983). Its size and complexity have presented a particular challenge, and this chapter describes a novel combination of two imaging techniques. Interpretation of the resultant images has relied on the wealth of earlier data. The aim has been to use X-ray crystallography to determine atomic structures of individual protein components and electron microscopy (EM) to determine the low-resolution structure of the intact complex. By accurately positioning the atomic structures within the reconstructed EM density and performing difference imaging, high-resolution structural information on the 150 x 10⁶-Da complex has been obtained. In comparison with other mammalian viruses for which structures have been determined by X-ray crystallography alone, the adenovirus particle is much larger, roughly 18 times the mass of the picornaviruses (Rossmann et al. 1985; Hogle et al. 1985) and six times the mass of the polyoma virus SV40 (Liddington et al. 1991). Thus far, the atomic structure of only one complete adenovirus capsid component, hexon, has been determined (Roberts et al. 1986; Athappilly et al. 1994). An early low-resolution structure of hexon (Burnett et al. 1985) was used to develop a model for hexon packing in the adenovirus capsid (Burnett 1985).