Bacteriophage PRD1 contains a labile receptor-binding structure at each vertex

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Bacteriophage PRD1 shares structural similarities with adenovirus.
• Identifying minor capsid proteins in PRD1 is crucial for understanding its structure-function relationship.
• PRD1's membrane-containing nature and capsid proteins are key areas of investigation.

Purpose of the Study:

• To identify structural or functional analogs of adenovirus proteins within bacteriophage PRD1.
• To characterize the role of essential PRD1 gene XXXI and its protein product (P31) in viral capsid assembly and DNA packaging.
• To investigate the function of PRD1 vertex proteins in DNA delivery.

Main Methods:

• Mutagenesis of unassigned PRD1 genes to create amber mutants (e.g., sus525).
• Cloning, overexpression, and purification of the PRD1 gene XXXI product (P31).
• Analytical ultracentrifugation, gel filtration, cryo-electron microscopy, and image reconstruction.

Main Results:

• Identification and characterization of PRD1 protein P31 as a homopentamer essential for capsid integrity.
• Absence of P31 in sus525 mutant particles leads to the deficiency of coat proteins P5 and P2.
• Cryo-EM revealed that P5 and P2 are located at the capsid vertices, which are missing in sus525 particles.
• Sus525 particles package DNA but lose it upon purification, indicating labile vertex structures.

Conclusions:

• PRD1 protein P31 is a key component of the viral capsid vertices, analogous to adenovirus penton base.
• PRD1's labile vertex structures, unlike those in other dsDNA phages, may mediate DNA delivery.
• A symmetry mismatch between P2 and P31 is proposed to be analogous to the adenovirus penton base-receptor interaction, influencing DNA delivery.