Wild-Type Human Adenovirus (Serotype 32)

Adenovirus is a non-enveloped double-stranded DNA virus with a genome approximately 36 kb in length. Its capsid has a regular icosahedral structure with a diameter of about 80-110 nm. The capsid contains 240 hexons, 12 pentons, and 12 fibers, as well as other small proteins such as VI, VIII, IX, IIIa, and IVa2. The hexon is the main protein forming the 20 triangular faces of the viral capsid. The 12 vertices are complexes composed of 5 penton subunits and 3 fiber proteins. The 12 fibers extend from the capsid surface with the penton protein as the base, and the fiber tips form a knob region. The penton and the knob region of the fiber can bind to viral receptors on the cell surface, playing a crucial role in the process of viral infection.

The adenovirus genome exists as linear double-stranded DNA, tightly surrounded by protein VII and a small protein called mu, which act in a histone-like manner. Another protein, V, connects this DNA-protein complex and is linked to the viral capsid via protein VI. A specialized structure called the DNA terminal protein complex (DNA-TPC) is covalently bound to the 5′ end of each strand, and is closely related to adenovirus replication. The adenovirus genome has a 100 bp inverted terminal repeat (ITR) sequence at each end, which serves as the origin of replication. A packaging signal (ψ) of approximately 300 bp is located on the 3′ side of the left ITR, mediating the packaging of the adenovirus genome into the viral capsid. For adenovirus, only the approximately 0.5 kb sequence including the ITRs and the packaging signal (ψ) are cis-acting elements, meaning they must be carried by the adenovirus vector itself, while the other 30 or so proteins can be complemented in trans by helper viruses (or cells).