Poster Presentation 25th International Pathogenic Neisseria Conference 2026

The role of the FitAB toxin-antitoxin system in Neisseria gonorrhoeae (#015)

Willow Collier 1 , Emma Walker 2 , Joanna Hicks 2
  1. School of Science, Division of STEM, University of Waikato, Hamilton, New Zealand
  2. School of Pharmacy and Biomedical Science, Division of Health, University of Waikato, Hamilton, New Zealand

FitAB is a type II toxin-antitoxin (TA) system in Neisseria gonorrhoeae that regulates gonococcal trafficking into epithelial cells, with loss of the system enhancing the rate of intracellular bacterial trafficking.1 FitAB is part of the VapBC family, which is widely distributed in bacteria and archaea, playing important roles in stress responses and cellular regulation.2 In these systems, the antitoxin binds and neutralises the toxin, while also contributing to transcriptional regulation of the TA operon.2

The FitAB complex binds nucleic acids, with FitA-FitB-DNA interactions exhibiting conditional cooperativity dependent on the FitA:FitB ratio, an emerging regulatory mechanism in bacterial stress responses.3 Under stress conditions, degradation of the antitoxin, FitA, releases the toxin, FitB, a sequence-specific ribonuclease that cleaves target RNA within the cell, altering bacterial growth rates. Notably, the substrate preferences of FitB differs from those of other members of the VapC toxin family, suggesting that FitAB could influence a distinct subset of bacterial transcripts and modulate cellular processes unique to the dynamics of N. gonorrhoeae infection.

Previous research from the Hicks lab demonstrated that deletion of FitAB in N. gonorrhoeae alters the dynamics of type IV pilus antigenic variation, leading to increased attachment to and invasion of epithelial cells. These findings suggest that FitAB regulates pilE antigenic variation, impacting the bacterium's ability to adhere to and survive within epithelial cells, thereby enhancing its persistence and pathogenicity in the host.

This project aims to determine the mechanism by which FitAB influences intracellular trafficking and pilus antigenic variation of N. gonorrhoeae. To do this, we will determine if the DNA-binding activity of the FitAB complex or the ribonuclease activity of FitB is leading to altered pilus recombination. We will explore the role of the FitAB system in multiple gonococcal strains to investigate any strain-specific differences. We will identify potential DNA-binding sites of the FitAB complex using in vitro DNA-binding and sequencing approaches and develop an in vivo readout of FitB activity to validate its predicted RNase function. Comparative analysis of TA system distribution across Neisseria species indicates that pathogenic species carry more TA systems per strain and are more likely to carry FitAB.

  1. Hopper, S.; Wilbur, J. S.; Vasquez, B. L.; Larson, J.; Clary, S.; Mehr, I. J.; Seifert, H. S.; So, M. Isolation of Neisseria gonorrhoeae Mutants That Show Enhanced Trafficking across Polarized T84 Epithelial Monolayers. Infect. Immun. 2000, 68 (2), 896–905. https://doi.org/10.1128/iai.68.2.896-905.2000
  2. Yamaguchi, Y.; Park, J.-H.; Inouye, M. Toxin-Antitoxin Systems in Bacteria and Archaea. Annu. Rev. Genet. 2011, 45 (Volume 45, 2011), 61–79. https://doi.org/10.1146/annurev-genet-110410-132412.
  3. Mattison, K.; Wilbur, J. S.; So, M.; Brennan, R. G. Structure of FitAB from Neisseria Gonorrhoeae Bound to DNA Reveals a Tetramer of Toxin-Antitoxin Heterodimers Containing Pin Domains and Ribbon-Helix-Helix Motifs *. J. Biol. Chem. 2006, 281 (49), 37942–37951. https://doi.org/10.1074/jbc.M605198200.