TssK Is a Trimeric Cytoplasmic Protein Interacting with Components of Both Phage-like and Membrane Anchoring Complexes of the Type VI Secretion System

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Zoued, Abdelrahim | Durand, Eric | Bebeacua, Cecilia, C. | Brunet, Yannick, R | Douzi, Badreddine | Cambillau, Christian | Cascales, E. | Journet, Laure

Edité par CCSD ; American Society for Biochemistry and Molecular Biology -

International audience. The Type VI secretion system (T6SS) is a macromolecular machine that mediates bacteria-host or bacteria-bacteria interactions. The T6SS core apparatus assembles from 13 proteins that form two sub-assemblies: a phage-like complex and a trans-envelope complex. The Hcp, VgrG, TssE, and TssB/C subunits are structurally and functionally related to components of the tail of contractile bacteriophages. This phage-like structure is thought to be anchored to the membrane by a trans-envelope complex composed of the TssJ, TssL, and TssM proteins. However, how the two sub-complexes are connected remains unknown. Here we identify TssK, a protein that establishes contacts with the two T6SS sub-complexes through direct interactions with TssL, Hcp, and TssC. TssK is a cytoplasmic protein assembling trimers that display a three-armed shape, as revealed by TEM and SAXS analyses. Fluorescence microscopy experiments further demonstrate the requirement of TssK for sheath assembly. Our results suggest a central role for TssK by linking both complexes during T6SS assembly.

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