The capsid polyprotein VP90 self-assembles and undergoes a proteolytic cleavage by host caspases to yield the VP70 virions. This immature virion is composed of 180 VP70 subunits with 90 dimeric spikes and displays a T=3 icosahedral symmetry. The mature virion is obtained by further cleavages resulting in three structural proteins VP25, VP27 and VP34. This forms contains only 30 spikes located on the icosahedral 2-fold axes. Plays a role in the attachment to target host cell. This attachment induces virion internalization through clathrin-dependent endocytosis (By similarity). Specific enzymatic cleavages in vivo yield mature protein(s). VP90 acidic C-terminal domain is eliminated from the immature virion by host caspases during viral maturation giving rise to virions composed of VP70. Further tryptic cleavages occur resulting in the three structural proteins VP34, VP27 and VP25 and confering infectivity (By similarity). Belongs to the astroviridae capsid polyprotein family.