6gig
From Proteopedia
Structural insights into AapA1 toxin
Structural highlights
FunctionAAPA1_HELPY May be involved in response to oxidative stress (Probable). Toxic component of a type I toxin-antitoxin (TA) system. When overexpression is induced in situ in the absence of its cognate antisense RNA antitoxin IsoA1 it leads to cell growth arrest and cell death without lysis. Neutralized by IsoA1 RNA which forms an extensive duplex with the mRNA (PubMed:28077560, PubMed:31476357, PubMed:33229580). Binds artificial prokaryotic and eukaryotic lipid membranes, with 30-fold higher affinity for prokaryotic membranes. Molecular dynamics suggests the peptide penetrates the membrane leading to lipid reorganization and thinning of the bilayer (PubMed:31476357). Induction of toxin in the absence of antitoxin RNA causes a fast conversion of cells from spiral-shaped to coccoid forms; cells have no visible membrane defects and resemble wild-type 'aging coccoids'. Toxin causes a moderate decrease in membrane potential and ATP content and alterations in peptidoglycan muropeptide abundance; GlcNAc-MurNAc dipeptides increase while GlcNAc-MurNAc tripeptides decrease (i.e. a faster phenocopy of cell aging). Deletion of all 6 AapA/IsoA TA loci in strain B128 leads to slower than wild-type conversion of H2O2-treated cells to the coccoid form. This suggests oxidative stress triggers coccoid transformation via these type I TA systems, although other factors eventually drive the morphology change (PubMed:33229580).[1] [2] [3] [4] Publication Abstract from PubMedBACKGROUND: We previously reported the identification of the aapA1/IsoA1 locus as part of a new family of toxin-antitoxin (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 alpha-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. Structural insights into the AapA1 toxin of Helicobacter pylori.,Korkut DN, Alves ID, Vogel A, Chabas S, Sharma CM, Martinez D, Loquet A, Salgado GF, Darfeuille F Biochim Biophys Acta Gen Subj. 2020 Jan;1864(1):129423. doi:, 10.1016/j.bbagen.2019.129423. Epub 2019 Aug 30. PMID:31476357[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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