Electron cryo-tomographic structure of cystovirus phi 12

Area of Science:

• Virology
• Structural Biology
• Microbiology

Background:

• Bacteriophage phi 12 belongs to the Cystoviridae family, possessing a double-stranded RNA (dsRNA) genome.
• Cystoviruses feature a phospholipid envelope with integral proteins, and their attachment mechanisms vary among species.
• Phi 12 utilizes a heteromeric protein complex (P3a and P3c) for attachment to rough lipopolysaccharide (rlps) receptors.

Purpose of the Study:

• To elucidate the 3D architecture of the intact bacteriophage phi 12.
• To identify and characterize the structural components involved in host cell attachment and viral entry.

Main Methods:

• Electron cryo-tomography was employed to determine the high-resolution 3D structure of bacteriophage phi 12.
• Analysis of the tomographic data allowed for visualization of the viral envelope, nucleocapsid, and protruding structures.

Main Results:

• The nucleocapsid of phi 12 is centrally located within the membrane envelope, potentially connected by bridging structures.
• Two distinct types of densities protrude from the viral envelope: elongated structures and a unique toroidal structure named 'the donut'.
• The 'donut' structure is connected to the envelope by a flexible stem and appears to play a role in inhibiting viral envelope fusion.

Conclusions:

• The study provides a detailed 3D structural model of bacteriophage phi 12, revealing its intricate organization.
• The identified 'donut' structure represents a novel viral component with potential implications for understanding viral entry mechanisms.
• Bacteriophage phi 12's unique attachment and potential fusion inhibition mechanisms offer insights into virus-host interactions within the Cystoviridae family.