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 undergoes a cascade of proteolytic cleavages presumably mediated by host caspases and extracellular proteases (By similarity). Belongs to the astroviridae capsid polyprotein family.