Baculovirus Per Os Infectivity Factor Complex: Components and Assembly.

Area of Science:

• Virology
• Molecular Biology
• Insect Pathology

Background:

• Baculovirus infection of insects relies on the per os infectivity factor (PIF) complex on occlusion-derived virions (ODVs).
• The precise composition and assembly of the PIF complex were previously not fully elucidated.

Purpose of the Study:

• To determine the complete protein composition of the PIF complex.
• To investigate the assembly process and identify the core components of the PIF complex.
• To understand the functional significance of PIF complex assembly for baculovirus oral infection.

Main Methods:

• Utilized blue native polyacrylamide gel electrophoresis, liquid chromatography-tandem mass spectrometry, and Western blotting.
• Employed synthetic baculovirus technology to individually knock out each PIF gene in Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV).
• Analyzed PIF complex formation in cellular fractions and its resistance to proteolytic degradation.

Main Results:

• Identified nine PIF proteins in the PIF complex, including a newly discovered PIF9, with a total molecular mass of approximately 500 kDa.
• Established a revised core complex of approximately 230 kDa, comprising PIF1, PIF2, and PIF3, challenging prior models.
• Demonstrated that PIF complex assembly initiates in the cytoplasm before nuclear transport and ODV envelope incorporation, with only the complete complex exhibiting proteolytic resistance.

Conclusions:

• The PIF complex consists of nine proteins, with a PIF1-3 core, and is assembled cytoplasmically prior to ODV envelope incorporation.
• Correct assembly of the full PIF complex is essential for baculovirus survival in the insect midgut.
• These findings provide a foundational understanding for future research into baculovirus ODV entry mechanisms.