Poxvirus host cell entry

Poxviruses are characterized by their large size, complex composition, and cytoplasmic life cycle. They produce two types of infectious particles: mature virions (MVs) and extracellular virions (EVs). Both MVs and EVs of vaccinia virus, the model poxvirus, take advantage of host cell endocytosis for internalization: they activate macropinocytosis — the most suitable form of endocytosis for large particles. Although largely dependent on the same cellular machinery, MV and EV entry differs with regard to the mechanisms used to trigger macropinocytosis and to undergo fusion. While EVs have to shed an additional membrane to expose the fusion complex, MV fusion requires the inactivation of fusion inhibitory proteins absent in EVs. This review highlights recent advances in the understanding of poxvirus MV and EV cell entry.

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► Poxviruses produce two infectious particles: mature virions (MVs) and extracellular virions (EVs).
► Both MVs and EVs bind to a variety of host cells using different attachment mechanisms.
► Both infectious forms induce their own endocytic uptake by macropincytosis.
► Fusion of the MV can be regulated by pH-sensitive fusion inhibitory proteins.
► The EV membrane is shed at low pH in macropinosomes to expose a fusogenic MV-like particle.