Mutations of cypovirus polyhedrin and applications of polyhedra to protein nanocontainers

Cypoviruses are insect viruses that produce micrometersized protein crystals called polyhedra. Virus particles are occluded in polyhedra. Recently we have developed a novel method for protein immobilization into polyhedra. It is possible to use these polyhedra to device ultra-stable protein nanocontainers. However, a weak point of them is that polyhedra dissolve only in high pH condition (pH>10.5). It seems important to carry out structure-based engineering of polyhedrin to derive mutants for multiple purposes. At a packing contact, we have identified a cluster of tyrosine (Fig. 1), deprotonation of which is likely to cause disruption of the lattice at alkaline pH. In this study, we substituted these tyrosine residues by other amino acids. We show that the substitutions of some residues in a cluster of tyrosine lead to modify a solubility of polyhedra. The results suggest that the modified polyhedra can serve as the basis for the development of nanoparticles for biotechnological applications.