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bioRxiv · 10.64898/2026.05.07.723447

Redox regulated auto-processing controls delivery of an antibacterial cysteine peptidase toxin

Hayes, C. S.·Nhan, D. Q.·Cuthbert, B. J.·Schroeder, K. A.·Hardy, C. D.·Garza-Sanchez, F.·Matthews, I. H.·Kennady, J. R.·Costello, M. S.·Goulding, C. W.
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Abstract

Contact-dependent growth inhibition (CDI) is a mechanism of inter-bacterial competition mediated by CdiA effectors, which deliver polymorphic C-terminal toxins (CT) into neighboring competitors. StbD from Citrobacter rodentium DBS100 is an unusual CdiA-like protein that carries a C-terminal cysteine peptidase toxin. Crystallography reveals that StbD-CT is composed of an N-terminal cytoplasm-entry domain connected to a C39 family peptidase by a flexible linker. The entry domain hijacks membrane-embedded YajC for translocation into the target-cell cytosol where the peptidase inactivates type II topoisomerases. Intoxication leads to a loss of DNA super-helicity, impaired chromosome segregation and cell filamentation. In addition to cleaving topoisomerases, StbD-CT exhibits auto-proteolytic processing under reducing conditions, and this activity is required for target cell intoxication. We propose that StbD-CT remains tethered to the cell periphery via interactions with YajC after delivery. Auto-processing releases the peptidase, enabling the domain to penetrate into the cell interior where it cleaves nucleoid-associated topoisomerases. Together, these findings identify a proteolytic effector that deactivates type II topoisomerases and reveal a redox regulatory strategy that coordinates toxin activation with intercellular delivery.

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Hayes, C. S., Nhan, D. Q., Cuthbert, B. J., Schroeder, K. A., Hardy, C. D., Garza-Sanchez, F., Matthews, I. H., Kennady, J. R., Costello, M. S., Goulding, C. W.. 2026-05-08. Redox regulated auto-processing controls delivery of an antibacterial cysteine peptidase toxin. https://doi.org/10.64898/2026.05.07.723447

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