Structural basis for assembly of vertical single β-barrel viruses

Area of Science:

• Structural Biology
• Virology
• Biochemistry

Background:

• The double beta-barrel major capsid protein (MCP) fold is characteristic of the PRD1-adenovirus viral lineage, found in viruses across all domains of life.
• The existence of PRD1-like viruses with two MCPs presented a challenge to established viral assembly principles.

Purpose of the Study:

• To elucidate the structural basis of viral assembly for archaeal viruses with double beta-barrel MCPs.
• To provide insights into the assembly mechanisms of viruses with membrane-less double beta-barrel MCPs.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures of Haloarcula californiae icosahedral virus 1 (HCIV-1) and Haloarcula hispanica icosahedral virus 2 (HHIV-2).
• Proteomics data were integrated with structural information.

Main Results:

• High-resolution (3.7 and 3.8 Å) cryo-EM structures of HCIV-1 and HHIV-2 were obtained.
• Structures revealed proteins beneath distinct two- and three-tower capsomers and homopentameric membrane proteins at vertices.
• These components orchestrate the positioning of pre-formed vertical single beta-barrel MCP heterodimers.

Conclusions:

• The study provides a detailed understanding of the assembly mechanism for HCIV-1 and HHIV-2.
• The findings contribute to understanding the assembly of viruses possessing double beta-barrel MCPs, including those without internal membranes.