Functional characterization of a pore‐forming effector TseMt from the H4 type VI secretion system of Pseudomonas aeruginosa

Abstract Pseudomonas aeruginosa is a major nosocomial pathogen in which the type VI secretion system (T6SS) contributes to interbacterial competition and virulence. While most strains encode three T6SSs, additional T6SS clusters have been identified in clinical isolates through comparative genomics, but their functions and effector biology remain undefined. Here, we identify TseMt as a major antibacterial effector associated with an H4‐T6SS in a clinical P. aeruginosa isolate LYSZa7. TseMt is a periplasmically active toxin whose activity is neutralized by a cognate immunity protein, TsiMt. Biochemical assays show that TseMt binds membranes and forms ion‐conducting pores, establishing it as a pore‐forming effector. A 3.0 Å cryo‐electron microscopy structure reveals a distinct three‐domain architecture comprising an N‐terminal MIX‐like domain, a central α‐helical scaffold, and a C‐terminal toxin domain. Genetic analysis and structural modeling indicate that TseMt is delivered through a dedicated PAAR−VgrG−chaperone pathway. Together, these findings define the structural basis, functional mechanism, and delivery pathway of the H4‐T6SS effector TseMt from a clinical P. aeruginosa isolate and reveal its role in mediating bacterial competition.