Portal Stability Controls Dynamics of DNA Ejection from Phage

Area of Science:

• Virology
• Biophysics
• Molecular Biology

Background:

• Bacteriophage lambda (λ) DNA ejection is a critical step in viral infection.
• Understanding the dynamics and regulation of this process is key to viral replication and control.

Purpose of the Study:

• To elucidate the mechanisms and dynamics of stochastic DNA ejection from phage λ.
• To investigate the role of receptor binding and thermal energy in initiating DNA ejection.
• To establish methods for studying virion stability under simulated cytoplasmic conditions.

Main Methods:

• Time-resolved single-molecule cryo-transmission electron microscopy (cryo-TEM).
• Bulk measurements including light scattering and small-angle X-ray scattering (SAXS).
• Analysis of activation energy barriers and temperature-dependent ejection rates.

Main Results:

• DNA ejection initiation requires both phage receptor (LamB) binding and capsid portal destabilization.
• A significant activation energy barrier (Ea ≈ 28 kTbody) for ejection initiation was quantified.
• Ejection rates increase 15-fold with a temperature rise from 15 °C to 45 °C, highlighting temperature sensitivity.
• A double fail-safe mechanism (receptor binding + energy barrier) ensures efficient ejection only under favorable conditions.

Conclusions:

• Phage λ employs a sophisticated dual mechanism for DNA ejection, optimizing infectivity based on temperature.
• This mechanism conserves infectious phage titer at suboptimal temperatures by inhibiting ejection.
• The study introduces a light scattering approach to assess capsid portal stability, relevant to virion deactivation dynamics.