Structural comparisons of some small spherical plant viruses

Area of Science:

• Structural virology
• Molecular evolution
• Biochemistry

Background:

• Plant viruses like tomato bushy stunt virus (TBSV), southern bean mosaic virus (SBMV), and satellite tobacco necrosis virus (STNV) possess icosahedral structures.
• Understanding the quantitative structural relationships between these viruses can illuminate their evolutionary pathways.

Purpose of the Study:

• To quantitatively compare the three-dimensional structures of TBSV, SBMV, and STNV.
• To identify conserved and divergent features in their coat protein structures and folding.
• To infer evolutionary relationships based on structural similarities and differences.

Main Methods:

• Quantitative structural analysis of TBSV, SBMV, and STNV.
• Comparison of icosahedral envelope organization and subunit packing.
• Analysis of polypeptide fold similarities, particularly the beta-sheet regions.
• Identification of conserved functional groups at the protein-RNA interface and other key sites.

Main Results:

• TBSV and SBMV exhibit identical organization of shell domains within their icosahedral envelopes.
• All three viruses share similarities in the beta-sheet region of their eight-stranded anti-parallel beta-barrel, but differ in subunit packing around specific axes.
• Conserved functional groups include threonines/serines at subunit ends, lysines/arginines at the protein-RNA interface, hydrophobic residues in the beta-barrel cavity, and ionic interactions between subunits.
• No clear homologous amino acid sequences were found between SBMV and STNV, though some functional group conservation exists.

Conclusions:

• TBSV and SBMV coat protein structures are more similar to each other than to STNV.
• Structural similarities and differences suggest a divergent evolutionary path for these viruses.
• Conserved functional groups may play critical roles in viral assembly and function across different virus families.