Structural studies of Chikungunya virus maturation

<jats:title>Significance</jats:title>
<jats:p>Chikungunya virus (CHIKV) belongs to the alphavirus family, the members of which have enveloped icosahedral capsids. The maturation process of alphaviruses involves proteolysis of some of the structural proteins before assembling with nucleocapsids to produce mature virions. We mutated the proteolytic cleavage site on E2 envelope protein, which is necessary in initiating the maturation process. Noninfectious virus-like particles (VLP) equivalent to “immature” fusion incompetent particles were produced to study the immature conformation of CHIKV. We describe the 6.8-Å resolution electron microscopy structure of “immature” CHIK VLPs. Structural differences between the mature and immature VLPs show that posttranslational processing of the envelope proteins and nucleocapsid is necessary to allow exposure of the fusion loop on glycoprotein E1 to produce an infectious virus.</jats:p>