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Structural insights into the AapA1 toxin of Helicobacter pylori

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Korkut, Dursun Nizam | Alves, Isabel, D. | Vogel, Alexander | Chabas, Sandrine | Sharma, Cynthia, M. | Martinez, Denis | Loquet, Antoine | Salgado, Gilmar | Darfeuille, Fabien

Edité par CCSD ; Elsevier -

International audience. Background: We previously reported the identification of the aapA1/IsoA1 locus as part of a new family of toxinantitoxin (TA) systems in the human pathogen Helicobacter pylori. AapA1 belongs to type I TA bacterial toxins, and both its mechanism of action towards the membrane and toxicity features are still unclear. Methods: The biochemical characterization of the AapA1 toxic peptide was carried out using plasmid-borne expression and mutational approaches to follow its toxicity and localization. Biophysical properties of the AapA1 interaction with lipid membranes were studied by solution and solid-state NMR spectroscopy, plasmon waveguide resonance (PWR) and molecular modeling. Results: We show that despite a low hydrophobic index, this toxin has a nanomolar affinity to the prokaryotic membrane. NMR spectroscopy reveals that the AapA1 toxin is structurally organized into three distinct domains: a positively charged disordered N-terminal domain (D), a single α-helix (H), and a basic C-terminal domain (R). The R domain interacts and destabilizes the membrane, while the H domain adopts a transmembrane conformation. These results were confirmed by alanine scanning of the minimal sequence required for toxicity. Conclusion: Our results have shown that specific amino acid residues along the H domain, as well as the R domain, are essential for the toxicity of the AapA1 toxin. General significance: Untangling and understanding the mechanism of action of small membrane-targeting toxins are difficult, but nevertheless contributes to a promising search and development of new antimicrobial drugs.

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