Palisade structure in intact vaccinia virions

Area of Science:

• Structural biology
• Virology
• Molecular biology

Background:

• Vaccinia virus assembly involves forming a biconcave core within the virion.
• The core boundary is defined by a pseudohexagonal palisade layer composed of trimers.
• Understanding this complex architecture is crucial for poxvirus research.

Purpose of the Study:

• To determine the subnanometer structure of the palisade trimer.
• To identify the viral proteins forming the palisade layer.
• To gain insights into vaccinia virus core assembly and organization.

Main Methods:

• Cryo-electron tomography and subtomogram averaging of purified vaccinia virions.
• AlphaFold2 structure predictions.
• Cellular localization assays.

Main Results:

• The palisade is formed by trimers of processed viral protein A10, associating with viral protein A4.
• The A4 N-terminus mediates interaction with A10, crucial for palisade association with the viral membrane.
• The palisade lattice incorporates hexameric portal structures, likely formed by viral protein E6.

Conclusions:

• The A10/A4 interaction provides insights into virion maturation.
• The widely spaced trimers allow for the biconcave core shape.
• Viral proteins A10, A4, and E6 are essential for vaccinia virus core formation and assembly.