Foamy virus capsids require the cognate envelope protein for particle export

Area of Science:

• Virology
• Molecular Biology
• Retroviruses

Background:

• Spumavirinae, including human foamy virus (HFV), uniquely require envelope (Env) glycoproteins for viral particle egress.
• Heterologous viral envelope proteins, such as murine leukemia virus (MuLV) Env and vesicular stomatitis virus G protein, fail to support HFV particle export.

Purpose of the Study:

• To investigate the specific domains of the HFV Env protein essential for viral particle envelopment, release, and infectivity.
• To determine if heterologous Env domains can restore function to deficient HFV Env mutants.

Main Methods:

• Analysis of deletion and point mutants of the HFV Env protein.
• Construction and testing of domain-swapping mutants using HFV, MuLV Env, and VSV-G proteins.
• Investigation of alternative membrane association strategies, including phosphoglycolipid anchors.

Main Results:

• The cytoplasmic domain (CyD) of HFV Env is dispensable for particle envelopment, release, and infectivity.
• Deletion of the membrane-spanning domain (MSD) of HFV Env results in cytoplasmic accumulation of naked capsids.
• Replacing the HFV MSD with the MuLV Env MSD facilitates budding at intracellular membranes, but virions remain non-infectious and unreleased.

Conclusions:

• The HFV Env protein possesses specific domains critical for efficient viral particle release and infectivity.
• The MSD is essential for proper viral egress, while the CyD plays a less critical role.
• Heterologous Env domains cannot fully rescue the release and infectivity defects of HFV mutants, highlighting species-specific requirements.