Biology subjects

Soscia, C.

Publications and source records attributed to Soscia, C..

3 recordsLinked to original sources

bioRxiv2026

The Type VI secretion effector TpeX expands the pore-forming virulence arsenal of Pseudomonas aeruginosa

The type VI secretion system (T6SS) is a major weapon used by Pseudomonas aeruginosa to antagonize competing bacteria through the delivery of a diverse repertoire of toxic effectors. Although several P. aeruginosa T6SS effectors target bacterial membranes, the mechanisms underlying membrane disruption remain poorly characterized. Here, we study TpeX (PA5265), an accessory T6SS effector from P. aeruginosa PAO1 with structural similarity to the VasX pore-forming effector of Vibrio cholerae. We show that membrane-targeted TpeX exerts a bactericidal activity in Escherichia coli, resulting in dissipation of the membrane potential and loss of membrane integrity. The TpeX C-terminal region containing the predicted colicin-like transmembrane domain is sufficient to confer toxicity, although with reduced activity, supporting its role as the membrane-disrupting module. TpeX also oligomerizes upon membrane targeting, forming at least dimers, and structural modelling predicts a membrane-embedded pore compatible with the observed permeabilization phenotype. We further identify TpiX (PA5264), the protein encoded by the downstream gene, as the cognate immunity protein, which partially protects cells from TpeX toxicity and interacts with TpeX. Finally, AlphaFold 3 modelling predicts an interaction between TpeX and the HcpB-VgrG6 T6SS spike, suggesting a possible mechanism for effector recruitment and delivery. Together, our results identify TpeX as a bactericidal, colicin-like pore-forming T6SS effector whose membrane activity is controlled by a cognate immunity protein, thereby expanding the repertoire of membrane-targeting weapons used by P. aeruginosa in interbacterial competition.

microbiology↗

bioRxiv2025

Molecular Insights into the bactericidal Toxin Tle1 of Pseudomonas aeruginosa: Interaction with VgrG, its adaptor, and immunity protein

The Type VI secretion system (T6SS) delivers a wide range of antibacterial effectors, including phospholipases of the Tle family. Here, we characterize Tle1 from Pseudomonas aeruginosa and demonstrate that it functions as a bactericidal toxin with moderate activity when associated to the membranes in the periplasm. Bacterial two-hybrid assays revealed specific protein-protein interactions within the tle1 locus, involving the immunity protein Tli1a, the chaperone/adaptor Tla1, and the spike protein VgrG4a. These interactions were independently validated by co-purification assays. Structural modeling with AlphaFold 3 produced a high-confidence ternary complex in which a VgrG4a trimer accommodates one Tle1 monomer and one Tla1 monomer. The three predicted interfaces (Tle1-Tla1, Tla1-VgrG4a, and Tle1-VgrG4a) were confirmed experimentally in vivo and important charged residues mediating these interfaces were identified. Furthermore, modeling of the Tle1-Tli1a complex suggests an inhibition mechanism that does not occlude the catalytic pocket. Consistently, Tli1a was localized to the outer membrane of P. aeruginosa, supporting in silico predictions of an outer membrane lipoprotein and positioning it ideally to neutralize periplasmic Tle1 activity. We did not observe the second candidate immunity protein, Tli1b, either in P. aeruginosa or in E. coli. Together, these findings elucidate the molecular interactions underlying Tle1 delivery and inhibition and highlight the role of Tli1a as a dedicated immunity protein that protects P. aeruginosa from self-intoxication.

microbiology↗

bioRxiv2019

A T6SS trans-kingdom effector is required for the delivery of a novel antibacterial toxin in Pseudomonas aeruginosa

Pseudomonas aeruginosa has evolved multiple strategies to disarm and take advantage of its host. For this purpose this opportunist pathogen has particularly developed protein secretion in the surrounding medium or injection into host cells. Among this, the Type VI Secretion System (T6SS) is utilized to deliver effectors into eukaryotic host as well as target bacteria. It assembles into a contractile bacteriophage tail-like structure that functions like a crossbow, injecting an arrow loaded with effectors into the target cell. The repertoire of T6SS antibacterial effectors of P. aeruginosa is remarkably broad to promote environmental adaptation and survival in various bacterial communities, and presumably in the eukaryotic host too. Here we report the discovery a novel pair of antibacterial effector and immunity of P. aeruginosa, Tle3 and Tli3. Tli3 neutralizes the toxicity of Tle3 in the periplasm to protect from fratricide intoxication. The characterization of the secretion mechanism of Tle3 indicates that it requires a cytoplasmic adaptor, Tla3, to be targeted and loaded onto the VgrG2b spike and thus delivered by the H2-T6SS machinery. Tla3 is different from the other adaptors discovered so far, and defines a novel family among T6SS. Interestingly this led us to discover that VgrG2b that we previously characterized as an anti-eukaryotic effector possesses an antibacterial activity as well, as it is toxic towards Escherichia coli. VgrG2b is thus a novel trans-kingdom effector targeting both bacteria and eukaryotes. VgrG2b represents an interesting target for fighting against P. aeruginosa in the environment and in the context of host infection. HighlightsO_LITle3 and Tli3 are a novel pair of antibacterial toxin and immunity of P. aeruginosa C_LIO_LITla3 recruits Tle3 in the cytoplasm, and targets it to VgrG2b C_LIO_LIVgrG2b is required for Tle3 delivery into target bacteria by the H2-T6SS C_LIO_LITla3 defines a novel type of T6SS adaptor with a DUF2875 C_LIO_LIVgrG2b is a new trans-kingdom effector targeting both bacteria and eukaryotes C_LI

microbiology↗