Cell width dictates Type VI secretion tail length

International audienceThe type VI secretion system (T6SS) is a multiprotein apparatus that injects protein effectors into target cells, hence playing a critical role in pathogenesis and in microbial communities [1, 2, 3, 4]. The T6SS belongs to the broad family of ontractile injection systems (CISs), such as Myoviridae bacteriophages and R-pyocins, that use a spring-like tail to propel a needle loaded with effectors [5, 6]. The T6SS tail comprises an assembly baseplate on which polymerizes a needle, made of stacked Hcp hexamers, tipped by the VgrG-PAAR spike complex and wrapped by the contractile sheath made of TssB and TssC [7, 8, 9, 10, 11, 12, 13]. The T6SS tail is anchored to the cell envelope by a membrane complex that also serves as channel for the passage of the needle upon sheath contraction [14, 15, 16]. In most CISs, the length of the tail sheath is invariable and is usually ensured by a dedicated protein called tape measure protein (TMP) [17, 18, 19, 20, 21, 22]. Here, we show that the length of the T6SS tail is constant in enteroaggregative Escherichia coli cells, suggesting that it is strictly controlled. By overproducing T6SS tail subunits, we demonstrate that component stoichiometry does not participate to the regulation of tail length. The observation of longer T6SS tails when the apparatus is relocalized at the cell pole further shows that tail length is not controlled by a TMP. Finally, we show that tail stops its elongation when in contact with the opposite membrane and thus that T6SS tail length is determined by the cell width

Structure and Activity of the Type VI Secretion System

International audienceThe type VI secretion system (T6SS) is a multiprotein machine that uses a spring-like mechanism to inject effectors into target cells. The injection apparatus is composed of a baseplate on which is built a contractile tail tube/sheath complex. The inner tube, topped by the spike complex, is propelled outside of the cell by the contraction of the sheath. The injection system is anchored to the cell envelope and oriented towards the cell exterior by a trans-envelope complex. Effectors delivered by the T6SS are loaded within the inner tube or on the spike complex and can target prokaryotic and/or eukaryotic cells. Here we summarize the structure, assembly, and mechanism of action of the T6SS. We also review the function of effectors and their mode of recruitment and delivery

In vivo TssA proximity labeling reveals temporal interactions during Type VI secretion 1 biogenesis and TagA, a protein that stops and holds the sheath.

International audienceThe Type VI secretion system (T6SS) is a multiprotein weapon used by bacteria to destroy competitor cells. The T6SS contractile sheath wraps an effector-loaded syringe that is injected into the target cell. This tail structure assembles onto the baseplate that is docked to the membrane complex. In entero-aggregative Escherichia coli TssA plays a central role at each stage of the T6SS assembly pathway by stabilizing the baseplate and coordinating the polymerization of the tail. Here we adapted an assay based on APEX2-dependent biotinylation to identify the proximity partners of TssA in vivo. By using stage-blocking mutations, we define the temporal contacts of TssA during T6SS biogenesis. This proteomic mapping approach also revealed an additional partner of TssA, TagA. We show that TagA is a cytosolic protein tightly associated with the membrane. Analyses of sheath dynamics further demonstrate that TagA captures the distal end of the sheath to stop its polymerization and to maintain it under the extended conformation

A β Strand Lock Exchange for Signal Transduction in TonB-Dependent Transducers on the Basis of a Common Structural Motif

SummaryTransport of molecules larger than 600 Da across the outer membrane involves TonB-dependent receptors and TonB-ExbB-ExbD of the inner membrane. The transport is energy consuming, and involves direct interactions between a short N-terminal sequence of receptor, called the TonB box, and TonB. We solved the structure of the ferric pyoverdine (Pvd-Fe) outer membrane receptor FpvA from Pseudomonas aeruginosa in its apo form. Structure analyses show that residues of the TonB box are in a β strand which interacts through a mixed four-stranded β sheet with the periplasmic signaling domain involved in interactions with an inner membrane sigma regulator. In this conformation, the TonB box cannot form a four-stranded β sheet with TonB. The FhuA-TonB or BtuB-TonB structures show that the TonB-FpvA interactions require a conformational change which involves a β strand lock-exchange mechanism. This mechanism is compatible with movements of the periplasmic domain deduced from crystallographic analyses of FpvA, FpvA-Pvd, and FpvA-Pvd-Fe

Tryptophan-mediated Dimerization of the TssL Transmembrane Anchor Is Required for Type VI Secretion System Activity

International audienc

Identification of Effectors: Precipitation of Supernatant Material

International audienc

Le système Tol/Pal d'Escherichia coli (Rôle de la protéine ToIR dans le maintien de l'intégrité de la membrane externe et dans l'importation des colicines)

AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Activity, delivery and diversity of Type VI secretion effectors

International audienceThe bacterial type VI secretion system (T6SS) system is a contractile secretion apparatus that delivers proteins to neighbouring bacterial or eukaryotic cells. Antibacterial effectors are mostly toxins that inhibit growth of other species and help to dominate the niche. A broad variety of these toxins cause cell lysis of the prey cell by disrupting the cell envelope. Other effectors are delivered into the cytoplasm where they affect DNA integrity, cell division or exhaust energy resources. The modular nature of T6SS machinery allows different means of recruitment of toxic effectors to secreted inner tube and spike components that act as carriers. Toxic effectors can be translationally fused to the secreted components or interact with them through specialized structural domains. These interactions can also be assisted by dedicated chaperone proteins. Moreover, conserved sequence motifs in effector-associated domains are subject to genetic rearrangements and therefore engage in diversification of the arsenal of toxic effectors. This review discusses the diversity of T6SS secreted toxins and presents current knowledge about their loading on the T6SS machinery

The Type VI Secretion System in Escherichia coli and Related Species.

International audienceThe type VI secretion system (T6SS) is a multiprotein complex widespread in Proteobacteria and dedicated to the delivery of toxins into both prokaryotic and eukaryotic cells. It thus participates in interbacterial competition as well as pathogenesis. The T6SS is a contractile weapon, related to the injection apparatus of contractile tailed bacteriophages. Basically, it assembles an inner tube wrapped by a sheath-like structure and anchored to the cell envelope via a membrane complex. The energy released by the contraction of the sheath propels the inner tube through the membrane channel and toward the target cell. Although the assembly and the mechanism of action are conserved across species, the repertoire of secreted toxins and the diversity of the regulatory mechanisms and of target cells make the T6SS a highly versatile secretion system. The T6SS is particularly represented in Escherichia coli pathotypes and Salmonella serotypes. In this review we summarize the current knowledge regarding the prevalence, the assembly, the regulation, and the roles of the T6SS in E. coli, Salmonella, and related species