Binding-induced stabilization and assembly of the phage P22 tail accessory factor gp4

Area of Science:

• Bacteriophage biology
• Molecular machines
• Structural biology

Background:

• Bacteriophage P22 infects Salmonella enterica serovar Typhimurium by injecting its genome.
• The phage tail complex, composed of five proteins, mediates host cell attachment and DNA injection.
• Tail accessory factors, including gp4, are crucial components of this molecular machine.

Purpose of the Study:

• To isolate and characterize the tail accessory factor gp4.
• To investigate the structural stability and binding interactions of gp4 with the portal protein (gp1).
• To elucidate the role of gp4 in the P22 virion assembly and DNA injection process.

Main Methods:

• Protein isolation and purification of gp4.
• Structural stability assays (Tm determination).
• Analysis of gp4 aggregation propensity.
• Investigation of gp4-portal protein interactions using native gel electrophoresis.
• Electron microscopy of the final complex.

Main Results:

• Isolated gp4 exists as a monomer with low structural stability (Tm 34°C) and aggregates readily.
• The dodecameric portal protein (gp1) stabilizes gp4, preventing aggregation and inducing oligomerization into a ring structure.
• A gp(1)12:gp(4)6 intermediate and a final bi-dodecameric gp(1)12:gp(4)12 complex were identified.
• Electron microscopy suggests gp4 acts as a structural adaptor, not a DNA channel plug.

Conclusions:

• The portal protein is essential for stabilizing the tail accessory factor gp4 within the P22 virion.
• gp4 oligomerizes upon binding to the portal protein, forming a key structural component of the tail complex.
• gp4 functions as a structural adaptor, facilitating the assembly and function of other tail accessory factors (gp10, gp26) for DNA injection.