Deltabaculoviruses encode a functional type I budded virus envelope fusion protein

Area of Science:

• Virology
• Molecular Biology
• Insect Pathology

Background:

• Baculoviridae family includes alpha-, beta-, and gammabaculoviruses.
• Envelope fusion (F) proteins are crucial for alpha- and betabaculovirus systemic infection.
• Gammabaculoviruses lack F protein homologues.

Purpose of the Study:

• To characterize the putative F-homologue (Cuni-F) from Culex nigripalpus nucleopolyhedrovirus (CuniNPV), a deltabaculovirus.
• To determine the function and properties of Cuni-F.

Main Methods:

• Expression of Cuni-F in insect cells.
• Analysis of Cuni-F localization and cell-cell fusion induction.
• Incorporation of Cuni-F into budded viruses (BVs) using a recombinant alphabaculovirus.
• Western blot analysis to detect Cuni-F cleavage forms.
• Tunicamycin treatment to assess N-glycosylation.
• Site-directed mutagenesis to identify the furin cleavage site.

Main Results:

• Cuni-F localizes to the cell surface and induces cell-cell fusion when expressed alone.
• Cuni-F is incorporated into BVs when expressed in an alphabaculovirus.
• Western blots revealed uncleaved (F0) and furin-cleaved (F1) forms of Cuni-F.
• Tunicamycin treatment confirmed N-glycans on Cuni-F.
• Mutagenesis identified the RARR motif (126–129) as the furin cleavage site.

Conclusions:

• CuniNPV encodes a functional F protein, Cuni-F.
• Cuni-F possesses properties characteristic of baculovirus F proteins, including cell fusion and BV incorporation.
• The identified furin cleavage site is essential for Cuni-F processing in insect cells.
• This finding expands the understanding of F protein function across different baculovirus genera.