Variable Assembly and Procapsid Binding of Bacteriophage P22 Terminase Subunits in Solution

Area of Science:

• Molecular biology
• Virology
• Structural biology

Background:

• Bacteriophage P22 utilizes a headful packaging mechanism for concatemeric viral DNA.
• This process is mediated by a terminase molecular machine composed of small (gp3) and large (gp2) subunits.
• The interaction of the terminase holoenzyme with the dodecameric portal protein at the procapsid vertex remains unclear.

Purpose of the Study:

• To elucidate the assembly states and conformations of the bacteriophage P22 terminase holoenzyme.
• To investigate the interaction of the terminase complex with procapsids.

Main Methods:

• Native mass spectrometry
• Transmission electron microscopy
• Native agarose gel electrophoresis

Main Results:

• The P22 terminase complex adopts three primary assembly states: 1(gp3)9:2(gp2), 2(gp3)9:5(gp2), and 3(gp3)9:7(gp2).
• These assemblies involve varying ratios of nonameric S-terminase (gp3) and L-terminase (gp2) subunits.
• The terminase complex interacts with procapsids through mild crosslinking, indicating conformational flexibility.

Conclusions:

• The bacteriophage P22 terminase complex is conformationally dynamic and can exist in multiple assembly states.
• Understanding these states is crucial for comprehending the mechanism of viral DNA packaging.