Vibrio parahaemolyticus prey targeting requires autoproteolysis-triggered dimerization of the type VI secretion system effector RhsP

The rearrangement hotspot (Rhs) repeat is an ancient giant protein fold found in all domains of life. Rhs proteins are polymorphic toxins that could either be deployed as an ABC complex or via a type VI secretion system (T6SS) in interbacterial competitions. To explore the mechanism of T6SS-delivered Rhs toxins, we used the gastroen-teritis-associated Vibrio parahaemolyticusas a model organism and identified an Rhs toxin-immunity pair, RhsP-RhsPI. Our data show that RhsP-dependent prey targeting by V. parahaemolyticus requires T6SS2. RhsP can bind to VgrG2 independently without a chaperone and spontaneously self-cleaves into three fragments. The toxic C-terminal fragment (RhsPC) can bind to VgrG2 via a VgrG2-interacting region (VIR). Our electron micro-scopy (EM)analysis reveals that the VIR is encapsulated inside the Rhs b barrel structure and that autoproteolysis triggers a dramatic conformational change of the VIR. This alternative VIR conformation promotes RhsP dimer-ization, which significantly contributes to T6SS2-mediated prey targeting by V. parahaemolyticus.

Automated summary

The study reveals that Rhs proteins, an ancient giant protein fold, can act as polymorphic toxins in interbacterial competitions through the ABC complex or T6SS. The research on Vibrio parahaemolyticus shows that RhsP-dependent prey targeting requires T6SS2 and RhsP can self-cleave into fragments, with the toxic C-terminal fragment binding to VgrG2. The alternative conformation of VIR, encapsulated inside the Rhs b barrel structure, triggers RhsP dimerization and plays a significant role in prey targeting.