Adenoviruses can replicate and produce disease in the respiratory, gastrointestinal, and urinary tracts and in the eye. Many adenovirus infections are subclinical, and virus may persist in the host for months. About one-third of the 57 known human serotypes are responsible for most cases of human adenovirus disease. A few types serve as models for cancer induction in animals. Adenoviruses are especially valuable systems for molecular and biochemical studies of eukaryotic cell processes. They are also useful vectors for gene therapy approaches.
PROPERTIES OF ADENOVIRUSES
Important properties of adenoviruses are listed in Table 32-1.
TABLE 32-1Important Properties of Adenoviruses ||Download (.pdf) TABLE 32-1 Important Properties of Adenoviruses
|Virion: Icosahedral, 70–90 nm in diameter, 252 capsomeres; fiber projects from each vertex |
|Composition: DNA (13%), protein (87%) |
|Genome: Double-stranded DNA, linear, 26–45 kbp, protein bound to termini, infectious |
|Proteins: Important antigens (hexon, penton base, fiber) are associated with the major outer capsid proteins |
|Envelope: None |
|Replication: Nucleus |
|Outstanding characteristic: Excellent models for molecular studies of eukaryotic cell processes |
Structure and Composition
Adenoviruses are 70–90 nm in diameter and display icosahedral symmetry, with capsids composed of 252 capsomeres. There is no envelope. Adenoviruses are unique among icosahedral viruses in that they have a structure called a “fiber” projecting from each of the 12 vertices, or penton bases (Figures 32-1 and 32-2). The rest of the capsid is composed of 240 hexon capsomeres. The hexons, pentons, and fibers constitute the major adenovirus antigens important in viral classification.
Electron micrographs of adenovirus. A: The viral particle displays cubic symmetry and is nonenveloped. A hexon capsomere (surrounded by six identical hexons) and a penton capsomere (surrounded by five hexons) are marked with dots. B: Note the fiber structures projecting from the vertex penton capsomeres (285,000×). (Reproduced with permission from Valentine RC, Pereira HG: Antigens and structure of the adenovirus. J Mol Biol 1965;13:13.)
Models of the adenovirus virion. A: A three-dimensional image reconstruction of an intact adenovirus particle showing fibers projecting from the penton bases. (Reproduced with permission from Liu H, Wu L, Zhou ZH: Model of the trimeric fiber and its interactions with the pentameric penton base of human adenovirus by cryo-electron microscopy. J Mol Biol 2011;406:764. [Graphical abstract.] Copyright Elsevier.) B: A stylized section of the adenovirus particle showing polypeptide components and DNA. No real section of the icosahedral virion would contain all components. Virion constituents are designated by their polypeptide numbers with the exception of the terminal protein (TP). (Reproduced with permission from Stewart PL, Burnett RM: Adenovirus structure as revealed by x-ray crystallography, electron microscopy and difference imaging. Jpn J Appl Phys 1993;32:1342.)