A viral genome packaging ring-ATPase is a flexibly coordinated pentamer.

Area of Science:

• Molecular biology
• Biophysics
• Structural biology

Background:

• Multi-subunit ring-ATPases are vital molecular motors involved in numerous cellular processes, including viral genome packaging.
• The precise mechanisms governing the ATPase activity and coordinated function of these motors remain largely unknown.
• Understanding these motors is crucial for deciphering viral replication strategies and developing antiviral therapies.

Purpose of the Study:

• To investigate the functional impact of ATPase-defective subunits on the bacteriophage T4 DNA packaging motor.
• To determine the minimum requirements for motor coordination and DNA translocation efficiency.
• To elucidate the role of subunit coordination in the function of viral DNA packaging motors.

Main Methods:

• Single-molecule fluorescence microscopy was employed to analyze the activity of individual bacteriophage T4 DNA packaging motors.
• Motors were systematically engineered with varying proportions of active and ATPase-defective gp17 subunits.
• The number of active/inactive subunits was precisely controlled to assess their impact on motor performance.

Main Results:

• The bacteriophage T4 DNA packaging motor was found to be composed of five gp17 subunits.
• Motors demonstrated tolerance to the presence of one or more ATPase-defective subunits.
• Inclusion of inactive subunits led to reduced DNA engagements, increased failure rates, slower packaging velocity, and more frequent pausing.

Conclusions:

• The bacteriophage T4 DNA packaging motor can compensate for inactive subunits by adjusting its DNA grip and resuming translocation.
• Strict coordination among motor subunits is not essential for efficient DNA packaging.
• These findings propose a flexible model for viral DNA packaging motor function, highlighting adaptability over rigid coordination.