Adenovirus Architecture

Abstract

The adenovirus family consists of related viruses infectious to several different mammalian and avian hosts (Ginsberg, 1984). The simple icosahedral shape of the virion (Fig. 1), with the characteristic fibres projecting from the capsid vertices, conceals a complex organisation. The particle contains approximately 2700 copies of at least 10 different polypeptides (van Oostrum and Burnett, 1985) and a single linear copy of double stranded DNA. Electron micrographs show 252 morphological units, which correspond to the major coat proteins penton and hexon. Penton, a complex between penton base AND fibre, lies at each of the 12 vertices where it is surrounded by 5 peripentonal hexons. The 20 facets and 30 edges of the icosahedral capsid are formed from 240 trimeric hexons, which contain the majority of the immunological determinants distinguishing the different adenoviral species. Dissociation of the virus releases first the 12 penton and their 60 surrounding peripentonal hexons to free 20 planar group-of-nine hexons (Fig. 1). The size of the virion, which is twentyfold larger than the RNA viruses whose structure are emerging currently (as reported elsewhere in these proceedings), has so far prohibited a direct X-ray crystallographic structure analysis of the complete particle. Our approach to understanding adenovirus has been through conbining structure determination for hexon with complementary studies of the virion and group-of-nine hexons using electron microscopy and biochemistry. Structural studies on hexon have been reviewed recently (Burnett, 1984).