Capsid protein (Cap)
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Function
- self-assembles to form the virion icosahedral capsid with a T=1 symmetry
- very small capsid (17-22 nm in diameter) allows the virus to be very stable in the environment & resistant to some disinfectants, including detergents
- essential for the initial attachment to heparan sulfate moieties & chondroitin sulfate B of the host cell surface proteoglycans
- after attachment, the virus is endocytosed & traffics to the nucleus
- the capsid protein binds & transports the viral genome & rep across the nuclear envelope
- homomultimer assembles in the nucleus, presumably in an immature form, then migrates to the cytoplasm once assembled as mature virion
- interacts with rep; this interaction relocates rep into the nucleus
Structure
- belongs to the circoviridae capsid protein family