Structural morphing in a symmetry-mismatched viral vertex

Area of Science:

• Structural biology
• Virology
• Biophysics

Background:

• Biological structures often assemble from symmetric subunits, but functional asymmetry is crucial.
• Many icosahedral viruses utilize a 12-fold symmetric portal complex within a 5-fold symmetric capsid vertex.
• This portal vertex plays key roles in viral processes like DNA packaging and genome ejection.

Purpose of the Study:

• To determine the near-atomic in situ structure of the symmetry-mismatched portal vertex in bacteriophage T4.
• To understand how structural asymmetry is accommodated at the interface between the portal complex and the capsid.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for near-atomic structural determination.
• In situ structural analysis of the bacteriophage T4 portal vertex.

Main Results:

• The bacteriophage T4 portal vertex exhibits a unique symmetry mismatch between its 12-fold symmetric portal and the 5-fold symmetric capsid vertex.
• Local structural adaptations within the portal complex compensate for the symmetry mismatch, maintaining specific interactions.
• The overall structure demonstrates a dynamic and adaptable symmetry-mismatched vertex critical for virion formation.

Conclusions:

• The bacteriophage T4 portal vertex is a dynamic, symmetry-mismatched structure essential for viral assembly.
• Structural plasticity allows the portal to adapt to different capsid environments while maintaining functional integrity.
• This study provides insights into the fundamental mechanisms of viral capsid assembly and maturation.