Interacts with VP7 to form the outer icosahedral capsid with an incomplete T=13 symmetry, about 80 nm in diameter, and consisting of 200 VP4-VP7 trimers. Myristoylated N-terminal peptide may be released in the endosome and involved in permeabilization and delivery of transcriptionally active viral particles into the host cell cytoplasm (Potential). Interacts with VP6 and VP7. Cleaved during the endosomal proteolytic disassembly of the outer capsid. N-terminally myristoylated. This acylation is essential for the membrane fusion activity (By similarity). Belongs to the aquareoviridae outer capsid VP4 protein family.