Structure–Function Analysis of the C-Terminal Domain of the Type VI Secretion TssB Tail Sheath Subunit. Issue 3 (2nd February 2018)

• Record Type: Journal Article
• Authors: Douzi, Badreddine; Logger, Laureen; Spinelli, Silvia; Blangy, Stéphanie; Cambillau, Christian; Cascales, Eric
• Is Part Of: Journal of molecular biology. Volume 430:Issue 3(2018)
• Page Start: 297
• Page End: 309
• Publication Date: 2018-02-02
• Subjects: T6SS type VI secretion system -- EAEC enteroaggregative Escherichia coli -- PCR polymerase chain reaction -- PDB Protein Data Bank; protein secretion -- structure -- X-ray -- contractile injection system -- sheath; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2017.11.015
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: The type VI secretion system (T6SS) is a specialized macromolecular complex dedicated to the delivery of protein effectors into both eukaryotic and bacterial cells. The general mechanism of action of the T6SS is similar to the injection of DNA by contractile bacteriophages. The cytoplasmic portion of the T6SS is evolutionarily, structurally and functionally related to the phage tail complex. It is composed of an inner tube made of stacked Hcp hexameric rings, engulfed within a sheath and built on a baseplate. This sheath undergoes cycles of extension and contraction, and the current model proposes that the sheath contraction propels the inner tube toward the target cell for effector delivery. The sheath comprises two subunits: TssB and TssC that polymerize under an extended conformation. Here, we show that isolated TssB forms trimers, and we report the crystal structure of a C-terminal fragment of TssB. This fragment comprises a long helix followed by a helical hairpin that presents surface-exposed charged residues. Site-directed mutagenesis coupled to functional assay further showed that these charges are required for proper assembly of the sheath. Positioning of these residues in the extended T6SS sheath structure suggests that they may mediate contacts with the baseplate. Graphical Abstract: Image 1 Highlights: Two regions are involved in T6SS sheath TssB protein oligomerization. The C-terminal domain of TssB is constituted of a long helix and a helical hairpin. Charged residues exposed at the surface of the hairpin are necessary for sheath assembly. TssB C-terminal domain protrudes toward the baseplate and likely contributes to tail attachment.