The Role of Flagellin B in Vibrio anguillarum -Induced Intestinal Immunity and Functional Domain Identification

, an opportunistic pathogen of aquatic animals, moves using a filament comprised of polymerised flagellin proteins. Flagellins are essential virulence factors for infection. Herein, we investigated the effects of flagellins ( , , , and ) on cell apoptosis, TLR5 expression, and production of IL-8 and TNF-α. exhibited the strongest immunostimulation effects. To explore the functions of in infection, we constructed a deletion mutant using a two-step recombination method, and experiments showed a significant decrease in the expression of TLR5 and inflammatory cytokines compared with wild-type cells. However in the study, expression of inflammatory cytokines and intestinal mucosal structure showed no significant differences between groups. Additionally, induced a significant increase in TLR5 expression based on microscopy analysis of fluorescently labelled TLR5, indicating interactions between the two proteins, which was confirmed by native PAGE and yeast two-hybrid assay. Molecular simulation of interactions between and TLR5 was performed to identify the residues involved in binding, revealing two binding sites. Then, based on molecular dynamics simulations, we carried out thirteen site-directed mutations occurring at the amino acid sites of Q57, N83, N87, R91, D94, E122, D152, N312, R313, N320, L97, H316, I324 in binding regions of protein by TLR5, respectively. Surface plasmon resonance (SPR) was employed to compare the affinities of mutants for TLR5, and D152, D94, I324, N87, R313, N320 and H316 were found to mediate interactions between and TLR5. Our comprehensive and systematic analysis of flagellins establishes the groundwork for future design of flagellin-based vaccines.