Abstract
Introduction. Entry of enveloped viruses into host cells requires binding of the virus to one or more receptors present at the host cell surface followed by fusion of the viral envelope with a cellular membrane. After binding, viruses such as paramyxoviruses, retroviruses and herpesviruses are thought to fuse directly with the plasma membrane. For other viruses, including the alpha-, rhabdo- and ortho-myxoviruses, binding does not directly lead to fusion. Instead, the bound virus particles are first internalized and then, at the low-pH within this compartment, fuse with the endosomal membrane.
In this review, we will focus on this latter class of viruses. For alpha-, rhabdo- and orthomyxoviruses, a glycoprotein is responsible for both virus attachment and fusion. In the acidic environment of the endosome, the ectodomain portion of the glycoprotein undergoes a major structural rearrangement to generate a fusion-competent state.