title: The HsiB1C1 (TssB-TssC) complex of the Pseudomonas aeruginosa type VI secretion system forms a bacteriophage tail sheathlike structure.
abstract: Protein secretion systems in Gram-negative bacteria evolved into a variety of molecular nanomachines. They are related to cell envelope complexes, which are involved in assembly of surface appendages or transport of solutes. They are classified as types, the most recent addition being the type VI secretion system (T6SS). The T6SS displays similarities to bacteriophage tail, which drives DNA injection into bacteria. The Hcp protein is related to the T4 bacteriophage tail tube protein gp19, whereas VgrG proteins structurally resemble the gp27/gp5 puncturing device of the phage. The tube and spike of the phage are pushed through the bacterial envelope upon contraction of a tail sheath composed of gp18. In Vibrio cholerae it was proposed that VipA and VipB assemble into a tail sheathlike structure. Here we confirm these previous data by showing that HsiB1 and HsiC1 of the Pseudomonas aeruginosa H1-T6SS assemble into tubules resulting from stacking of cogwheel-like structures showing predominantly 12-fold symmetry. The internal diameter of the cogwheels is ~100 Å, which is large enough to accommodate an Hcp tube whose external diameter has been reported to be 85 Å. The N-terminal 212 residues of HsiC1 are sufficient to form a stable complex with HsiB1, but the C terminus of HsiC1 is essential for the formation of the tubelike structure. Bioinformatics analysis suggests that HsiC1 displays similarities to gp18-like proteins in its C-terminal region. In conclusion, we provide further structural and mechanistic insights into the T6SS and show that a phage sheathlike structure is likely to be a conserved element across all T6SSs.
authors: Medical Research Council Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Nadine S
authors: NS
authors: Lossi
authors: Medical Research Council Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Eleni
authors: E
authors: Manoli
authors: Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Andreas
authors: A
authors: Förster
authors: Medical Research Council Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Rana
authors: R
authors: Dajani
authors: Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Tillmann
authors: T
authors: Pape
authors: Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Paul
authors: P
authors: Freemont
authors: Medical Research Council Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom. Electronic address: a.filloux@imperial.ac.uk.
authors: Alain
authors: A
authors: Filloux
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000502:physiology*; D058947:Bacterial Secretion Systems / Q000502:physiology*; D001435:Bacteriophages / Q000378:metabolism*; D019295:Computational Biology / Q000379:methods; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008854:Microscopy, Electron / Q000379:methods; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems