3D structure of three jumbo phage heads

Area of Science:

• Structural biology
• Virology
• Microbiology

Background:

• Jumbo phages are bacteriophages with large DNA genomes (>200 kbp).
• Understanding their structure is key to comprehending their replication and evolution.
• Cryo-electron microscopy provides high-resolution insights into viral architecture.

Purpose of the Study:

• To characterize the three-dimensional structures of jumbo phage capsids.
• To elucidate the geometric principles underlying their icosahedral capsid construction.
• To investigate the role of accessory proteins in capsid stability.

Main Methods:

• Cryo-electron microscopy was used to determine the structures of two jumbo phages (ΦRSL2, ΦXacN1) and one semi-jumbo phage (ΦRP13).
• Three-dimensional reconstructions of phage heads were calculated at 9–16 Å resolution.
• Analysis of the structures focused on capsid geometry and protein composition.

Main Results:

• Determined the 3D structures of ΦRSL2, ΦXacN1, and ΦRP13 capsids.
• Identified the geometrical basis of icosahedral capsid assembly, including accessory proteins.
• Discovered a novel triangulation number (T=21) for Myoviridae (ΦRP13) and common numbers (T=27, T=28) for jumbo phages.
• Provided evidence that accessory proteins are not essential for the structural integrity of very large capsids.

Conclusions:

• The study reveals the structural basis of jumbo phage capsid formation.
• Novel triangulation numbers were identified, expanding our understanding of viral evolution.
• The findings challenge the necessity of accessory proteins for maintaining the stability of large bacteriophage capsids.