Large terminase conformational change induced by connector binding in bacteriophage T7

Area of Science:

• Structural Biology
• Molecular Biology
• Virology

Background:

• DNA translocation into bacteriophage proheads is mediated by a portal protein-terminase complex.
• The terminase functions as a motor, converting ATP hydrolysis into mechanical DNA movement.

Purpose of the Study:

• To determine the structure of the T7 large terminase and the complete connector-terminase complex.
• To elucidate the molecular mechanisms underlying DNA translocation during bacteriophage T7 morphogenesis.

Main Methods:

• Electron microscopy was used to determine the structure of the T7 large terminase and the connector-terminase complex.
• Atomic modeling based on T4 phage terminase crystallographic structure was employed to understand conformational changes.

Main Results:

• The T7 terminase consists of five subunits forming a toroid with a channel for dsDNA.
• The complete connector-terminase complex forms a continuous channel, with the terminase exhibiting a different conformation compared to the isolated pentamer.
• Subunit rotation in the pentameric assembly explains the transition between the two observed terminase conformations.

Conclusions:

• The study reveals the structural basis of the T7 terminase motor and its interaction with the connector.
• Two distinct terminase conformations were identified, suggesting a mechanism for sequential DNA translocation.
• These findings provide molecular insights into the DNA packaging mechanism of bacteriophage T7.