Dissection of the TssB-TssC interface during type VI secretion sheath complex formation

• Published in: PloS one Vol. 8; no. 11; p. e81074
• Main Authors: Zhang, Xiang Y, Brunet, Yannick R, Logger, Laureen, Douzi, Badreddine, Cambillau, Christian, Journet, Laure, Cascales, Eric
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 25.11.2013; Public Library of Science (PLoS)
• Subjects: Bacteria; Bacteriophages - metabolism; Biochemistry; Biochemistry, Molecular Biology; Biophysics; Burkholderia cenocepacia; Cloning; Complex formation; Contractility; Contraction; Delivery contracts; Dissection; DNA methylation; E coli; Elongation; Escherichia coli; Fluorescence; Fluorescence microscopy; Francisella tularensis; Genes; HCP protein; Hydrophobicity; Life Sciences; Microscopy, Fluorescence; Molecular biology; Mutagenesis; Mutagenesis, Site-Directed; Phages; Proteins; Secretion; Signal transduction; Site-directed mutagenesis; Structural Biology; Toxins; Vibrio cholerae; Viral Proteins - genetics; Viral Proteins - metabolism; Yersinia pseudotuberculosis; France; Bacteriophages; Vibrio cholerae; Pseudomonas aeruginosa; Substitution mutation; Protein interactions; Protein structure; Fluorescence microscopy; Secretion systems
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0081074

The Type VI secretion system (T6SS) is a versatile machine that delivers toxins into either eukaryotic or bacterial cells. At a molecular level, the T6SS is composed of a membrane complex that anchors a long cytoplasmic tubular structure to the cell envelope. This structure is thought to resemble the tail of contractile bacteriophages. It is composed of the Hcp protein that assembles into hexameric rings stacked onto each other to form a tube similar to the phage tail tube. This tube is proposed to be wrapped by a structure called the sheath, composed of two proteins, TssB and TssC. It has been shown using fluorescence microscopy that the TssB and TssC proteins assemble into a tubular structure that cycles between long and short conformations suggesting that, similarly to the bacteriophage sheath, the T6SS sheath undergoes elongation and contraction events. The TssB and TssC proteins have been shown to interact and a specific α-helix of TssB is required for this interaction. Here, we confirm that the TssB and TssC proteins interact in enteroaggregative E. coli. We further show that this interaction requires the N-terminal region of TssC and the conserved α-helix of TssB. Using site-directed mutagenesis coupled to phenotypic analyses, we demonstrate that an hydrophobic motif located in the N-terminal region of this helix is required for interaction with TssC, sheath assembly and T6SS function.