Biology subjects

Altuna-Alvarez, J.

Publications and source records attributed to Altuna-Alvarez, J..

4 recordsLinked to original sources

bioRxiv2025

The cryo-EM structure of an adaptor-effector complex reveals the mechanism of a widespread pore-forming toxin family

Pseudomonas putida KT2440 is a plant-beneficial rhizobacterium that encodes multiple Type VI secretion systems (T6SS) to outcompete phytopathogens in the rhizosphere. Among its antibacterial effectors, Tke5 has been identified as a potent pore-forming toxin that disrupts ion homeostasis without causing considerable membrane damage. Tke5 belongs to the BTH_I2691 protein family and harbours an N-terminal marker for the type six secretion system effectors (MIX) motif, previously shown to be required for T6SS-dependent secretion in other systems. Many MIX-containing effectors require T6SS adaptor proteins (Tap) for secretion, but until now, the molecular mechanism for adaptor-effector binding has remained elusive. Here, we report the 2.8 [A] cryo-EM structure of the Tap3-Tke5 complex, providing structural and functional insight into how this effector is recruited by its cognate adaptor protein Tap3. Functional dissection shows that the -helical region of Tke5 is sufficient to kill intoxicated bacteria, while its {beta}-rich region likely contributes to target membrane specificity. These findings suggest a general mechanism of MIX-containing BTH_I2691 proteins for Tap recruitment and toxin activity, contributing to our fundamental understanding of a widespread yet understudied toxin family.

microbiology↗

bioRxiv2025

The Pseudomonas aeruginosa Tse4 toxin assembles ion-selective and voltage-sensitive ion channels to couple membrane depolarisation with K+ efflux

Pseudomonas aeruginosa employs the Type VI secretion system (T6SS) to outcompete other bacteria in its environment. Among the effectors secreted by the T6SS of P. aeruginosa PAO1, Tse4 is known for its potent antibacterial activity. This study elucidates the molecular function of Tse4, which promotes cell depolarisation in competing bacteria. Our results show that Tse4 spontaneously incorporates into lipid monolayers and forms multiionic channels in planar bilayers, with either ohmic conduction or diode-like rectifying currents and a preference for cations over anions. These observations allow us to propose a model of action whereby Tse4 channels couple cell depolarisation with K+ efflux. These insights into Tse4s pore-forming activity enhance our understanding of bacterial competition and exemplify a finely tuned antibacterial strategy, coupling its ability to cause membrane depolarisation with potassium efflux that synergises with other T6SS effectors. These results highlight the sophistication of Pseudomonas aeruginosas competitive arsenal.

microbiology↗

bioRxiv2025

Tke5 is a novel Pseudomonas putida toxin that depolarises membranes killing plant pathogens

The soil bacterium Pseudomonas putida injects toxic proteins into neighbouring competitors, including resilient phytopathogens, using the Type VI secretion system (T6SS). The secretion of toxins endows P. putida with a significant fitness advantage, allowing this biocontrol agent to thrive in plant-related polymicrobial environments and prevent phytopathogen infections. Despite its agricultural significance, the toxin repertoire of P. putida, particularly those secreted via the K2- and K3-T6SSs, remains poorly understood. We present the first comprehensive molecular study of Tke5, a potent toxin encoded within the K3-T6SS, which represents the first comprehensive functional analysis of the BTH_I2691 protein family. Our biophysical data demonstrate that Tke5 is a pore-forming toxin that disrupts bacterial membranes through selective ion transport, inducing membrane depolarisation and cell death. Unlike conventional detergent-like pore-forming toxins, Tke5 preserves overall membrane integrity, avoiding large, non-specific disruptions. This unique mechanism offers a powerful approach to targeting resilient phytopathogens. This study reveals a previously undescribed mode of action within a widespread yet understudied toxin family. Our findings highlight the potential of P. putida as a biocontrol agent, offering alternatives to chemical pesticides by exploiting novel toxin mechanisms. Understanding these bacterial toxins is crucial for developing effective strategies to combat plant pathogens.

microbiology↗

bioRxiv2024

WHIX is a T6SS secretion domain found in polymorphic double-edged sword effectors

Gram-negative bacteria employ the type VI secretion system (T6SS) to deliver toxic effectors into neighboring cells and outcompete rivals. Although many effectors have been identified, their secretion mechanism often remains unknown. Here, we describe WHIX, a domain that is sufficient to mediate the secretion of effectors via the T6SS. Remarkably, we find WHIX in T6SS effectors that contain a single toxic domain, as well as in effectors that contain two distinct toxic domains fused to either side of WHIX. We demonstrate that the latter, which we name double-edged sword effectors, require two cognate immunity proteins to antagonize their toxicity. Furthermore, we show that WHIX can be used as a chassis for T6SS-mediated secretion of multiple domains. Our findings reveal a new class of polymorphic T6SS cargo effectors with a unique secretion domain that can deploy two toxic domains in one shot, possibly reducing recipients ability to defend themselves.

microbiology↗