Characterization and Phylogenetic Insights into the First Viral Major Vault Proteins (MVPs), Identified in Bacteriophages from the Human Gut.

The Major Vault Protein (MVP) is the principal component of the enigmatic vault complex, dome-shaped cytoplasmic ribonucleoproteins found in eukaryotes. Although vaults have been associated with several minor functions, including amino acid storage and cargo transport, their overall function remains to be fully understood. While MVPs are widely distributed among most higher eukaryotes and have homologs in prokaryotes, no similar protein have been reported in viral species until now. In this study, we explored the NCBI viral protein database for MVP homologs and identified two putative MVPs from distinct tailed bacteriophage isolates from the Class Caudoviricetes, ctOa11 and ctRi15, of human gut metagenomic samples. Further in silico analysis were conducted to describe and characterize these unprecedent phage proteins. Phylogenetic topologies indicate that viral MVPs are closely related to bacterial MVP homologs. Tridimensional protein models of viral MVPs were generated to perform protein structure comparisons with eukaryotic and prokaryotic MVPs, indicating a significant similarity to bacterial proteins. For the functional significance of MVPs in phage infectivity, we suggest that they may have an unknown metabolic role enhancing phage fitness. While this work provides new insights into the genetic phage diversity and phylogenetic distribution of MVPs, complementary functional studies are necessary to fully elucidate their function in viral and bacterial species.