Giant viruses encode vitamin K-based redox modules for lipid modification

Area of Science:

• Virology
• Biochemistry
• Molecular Biology

Background:

• Giant viruses encode auxiliary metabolic genes impacting host physiology.
• The roles of these viral genes in host redox and membrane homeostasis are largely unknown.

Purpose of the Study:

• To identify and functionally characterize viral homologs of vitamin K epoxide reductase (VKOR) in giant viruses.
• To investigate the potential role of viral VKORs in modifying host membrane lipid composition and redox balance.

Main Methods:

• Phylogenetic and genomic context analysis of viral VKOR genes.
• Functional expression of viral VKORs in engineered *Escherichia coli* strains.
• Analysis of membrane topology, catalytic activity, and bacterial motility.
• Structural modeling and in vivo expression analysis during viral infection.

Main Results:

• Viral VKOR genes were identified and found to be co-located with genes for epoxidases and desaturases, suggesting a modular pathway.
• Reconstituted viral VKORs in *E. coli* acted as catalytically competent electron shuttles, restoring bacterial motility with minimal modifications.
• Structural modeling indicated potential integration into host endoplasmic reticulum-like environments.
• Viral VKORs and associated enzymes are expressed during *Fadolivirus* and *Yasminevirus* infections of *Vermamoeba vermiformis*.

Conclusions:

• Giant viruses encode functional VKOR enzymes that can be integrated into host cellular machinery.
• These viral VKORs represent a strategy for manipulating host redox metabolism and membrane lipid composition.
• The findings expand the known functions of giant viruses and their interaction with host membranes.