Salmonella YqiC exerts its function through an oligomeric state.

Protein oligomerization occurs frequently both in vitro and in vivo, with specific functionalities associated with different oligomeric states. The YqiC protein from Salmonella Typhimurium forms a homotrimer through its C-terminal coiled-coil domain, and the protein is closely linked to the colonization and invasion of the bacteria to the host cells. To elucidate the importance of the oligomeric state of YqiC in vivo and its relation with bacterial infection, we mutated crucial residues in YqiC's coiled-coil region and confirmed the loss of trimer formation using chemical crosslinking and size exclusion chromatography coupled with multiple angle light scattering (SEC-MALS) techniques. The yqiC-knockout strain complemented with mutant YqiC showed significantly reduced colonization and invasion of Salmonella to host cells, demonstrating the critical role of YqiC oligomerization in bacterial pathogenesis. Furthermore, we conducted a protein-protein interaction study of YqiC using a pulled-down assay coupled with mass spectrometry analysis to investigate the protein's role in bacterial virulence. The results reveal that YqiC interacts with subunits of Complex II of the electron transport chain (SdhA and SdhB) and the β-subunit of F F -ATP synthase. These interactions suggest that YqiC may modulate the energy production of Salmonella and subsequently affect the assembly of crucial virulence factors, such as flagella. Overall, our findings provide new insights into the molecular mechanisms of YqiC's role in S. Typhimurium pathogenesis and suggest potential therapeutic targets for bacterial infections.