Structural studies on the empty capsids of Physalis mottle virus

Area of Science:

• Structural biology
• Virology
• Biochemistry

Background:

• Physalis mottle virus (PMV) is a plant virus with an icosahedral capsid.
• Understanding the structural differences between empty and RNA-containing capsids is crucial for viral assembly and function.

Purpose of the Study:

• To determine the three-dimensional crystal structure of the empty Physalis mottle tymovirus capsid.
• To compare the structure of the empty capsid with the native, RNA-containing virus to understand structural changes upon RNA encapsidation.

Main Methods:

• X-ray crystallography at 3.2 A resolution.
• Structure determination using real-space electron-density averaging with a known PMV structure as a phasing model.
• Comparative analysis of empty and native capsid structures.

Main Results:

• The empty Physalis mottle tymovirus capsid structure was determined, revealing significant differences in N-terminal residues of subunits A, B, and C compared to the native virus.
• Empty capsids showed a radial expansion of approximately 1.8 A, with altered subunit orientations relative to symmetry axes.
• Pentamer-hexamer contacts were reduced in empty capsids, while the overall quaternary organization remained largely unchanged.

Conclusions:

• RNA encapsidation in Physalis mottle virus leads to a reduction in particle radius and ordering of N-terminal arms.
• The observed structural changes upon RNA encapsidation are more pronounced than in other studied viruses.
• These findings provide insights into the dynamic structural rearrangements during viral assembly.