Polyhedra structures and the evolution of the insect viruses

Area of Science:

• Structural biology
• Virology
• Evolutionary biology

Background:

• Polyhedra are ancient protein crystals protecting insect viruses.
• These structures are crucial for virion survival during environmental exposure.

Purpose of the Study:

• To determine high-resolution crystal structures of polyhedra from seven uncharacterized cypoviruses.
• To analyze the evolutionary conservation of polyhedrin structure and sequence.

Main Methods:

• X-ray crystallography
• Ab initio selenomethionine phasing
• Structural alignment and comparison of polyhedrin structures

Main Results:

• High-resolution structures of seven cypovirus polyhedra were determined.
• Polyhedrins exhibit high structural equivalence (~80% residues) despite low sequence identity (12%).
• Conserved crystal contacts across the molecular surface, excluding a virus recognition domain, ensure lattice robustness.

Conclusions:

• The crystal lattice, not the sequence, is the functionally conserved feature in polyhedrins.
• Evolutionary constraints favor conservation of surface contacts, maintaining lattice stability despite sequence variability.
• This suggests a unique evolutionary pathway driven by structural requirements for viral protection.