Protein component of the viral occlusion body, a crystalline protein matrix which surrounds the nucleocapsids of some insect viruses (baculoviridae, entomopoxvirinae, cypovirus). Viral occlusion bodies are produced either in the nucleus (baculoviridae) or in the cytoplasm (poxvirinae and cypovirus) of the infected cells and confer resistance to adverse environmental conditions on viruses. They are made from polyhedrin (nucleopolyhedrovirus, cypovirus), granulin (granulovirus), spheroidin and spherulin (entomopox-virinae) and are dissolved by the alkaline pH of the insect gut, thus resulting in the release of infectious virus particles.