| Many viruses go through a maturation step in the final stages of assembly before being transmitted to another host. The maturation process of flaviviruses is directed by the proteolytic cleavage of the precursor membrane protein (prM), which is associated with an extraordinary re-arrangement of the surface glycoproteins, turning the inert virus into an infectious particle. The crystal structure has been determined of a recombinant protein that links dengue virus prM with the envelope glycoprotein (E). The structure represents the prM-E heterodimer present in immature flaviviruses and fits well into the cryo-electron microscopy density that forms the 60 trimeric spikes of immature virus at neutral pH. The pr peptide beta-barrel structure covers the fusion loop in E, preventing fusion with host cell membranes. The prM-E structure provides a basis for identifying the stages of its pH-directed, conformational metamorphosis during maturation, ending with the release of pr when budding from the host. |
