scholarly journals Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones

2020 ◽  
Author(s):  
Shehryar Ahmad ◽  
Kara K. Tsang ◽  
Kartik Sachar ◽  
Dennis Quentin ◽  
Tahmid M. Tashin ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Effector Proteins ◽  
Structural Basis ◽  
Gram Negative Bacteria ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
Type Vi Secretion ◽  
Helical Packing ◽  
Target Cell Membrane ◽  
Abundance And Distribution

AbstractType VI secretion systems facilitate the delivery of antibacterial effector proteins between neighbouring Gram-negative bacteria. A subset of these effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across the target cell membrane. However, the abundance and distribution of these TMD-containing effectors has remained unknown. Here we report the discovery of prePAAR, a conserved motif found in over 6,000 putative TMD-containing effectors. Based on their differing sizes and number of TMDs these effectors fall into two distinct classes that are unified by their requirement for a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR functions to facilitate proper folding of the downstream PAAR domain, which is required for effector interaction with the T6SS spike. Taken together, our findings define the mechanism of chaperone-assisted secretion of a widespread family of T6SS membrane protein effectors.

scholarly journals Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Shehryar Ahmad ◽  
Kara K Tsang ◽  
Kartik Sachar ◽  
Dennis Quentin ◽  
Tahmid M Tashin ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Transmembrane Domain ◽  
Secretion System ◽  
Effector Proteins ◽  
Structural Basis ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
Conserved Motif ◽  
Type Vi Secretion ◽  
Helical Packing

Type VI secretion systems (T6SSs) deliver antibacterial effector proteins between neighboring bacteria. Many effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across target cell membranes. However, the distribution of these TMD-containing effectors remains unknown. Here, we discover prePAAR, a conserved motif found in over 6000 putative TMD-containing effectors encoded predominantly by 15 genera of Proteobacteria. Based on differing numbers of TMDs, effectors group into two distinct classes that both require a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR residues mediate effector-VgrG spike interactions. Taken together, our findings reveal mechanisms of chaperone-mediated stabilization and secretion of two distinct families of T6SS membrane protein effectors.

scholarly journals Diversification of the Type VI Secretion System in Agrobacteria

mBio ◽  
2021 ◽  
Author(s):  
Chih-Feng Wu ◽  
Alexandra J. Weisberg ◽  
Edward W. Davis ◽  
Lin Chou ◽  
Surtaz Khan ◽  
...  
Keyword(s):  
Secretion System ◽  
Effector Proteins ◽  
Gram Negative Bacteria ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Bacterial Interactions ◽  
Type Vi Secretion

The T6SS is used by several taxa of Gram-negative bacteria to secrete toxic effector proteins to attack others. Diversification of effector collections shapes bacterial interactions and impacts the health of hosts and ecosystems in which bacteria reside.

scholarly journals Structural Basis for Effector Transmembrane Domain Recognition by Type VI Secretion System Chaperones

2021 ◽  
Vol 35 (S1) ◽  
Author(s):  
John Whitney ◽  
Shehryar Ahmad ◽  
Kara Tsang ◽  
Kartik Sachar ◽  
Andrew McArthur ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Secretion System ◽  
Structural Basis ◽  
Type Vi Secretion System ◽  
Type Vi Secretion

scholarly journals A new family of Type VI secretion system-delivered effector proteins displays ion-selective pore-forming activity

2019 ◽  
Author(s):  
Giuseppina Mariano ◽  
Katharina Trunk ◽  
David J. Williams ◽  
Laura Monlezun ◽  
Henrik Strahl ◽  
...  
Keyword(s):  
Effector Proteins ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
New Family ◽  
Type Vi Secretion ◽  
Outer Membrane Permeability ◽  
Polymicrobial Communities ◽  
Bacterial Effectors

AbstractType VI secretion systems (T6SSs) are nanomachines widely used by bacteria to compete with rivals. T6SSs deliver multiple toxic effector proteins directly into neighbouring cells and play key roles in shaping diverse polymicrobial communities. A number of families of T6SS-dependent anti-bacterial effectors have been characterised, however the mode of action of others remains unknown. Here we report that Ssp6, an anti-bacterial effector delivered by theSerratia marcescensT6SS, is an ion-selective pore-forming toxin.In vivo, Ssp6 inhibits growth by causing depolarisation of the inner membrane of intoxicated cells and also leads to increased outer membrane permeability, whilst reconstruction of Ssp6 activityin vitrodemonstrated that it forms cation-selective pores. A survey of bacterial genomes revealed that Ssp6-like effectors are widespread in Enterobacteriaceae and often linked with T6SS genes. We conclude that Ssp6 represents a new family of T6SS-delivered anti-bacterial effectors, further diversifying the portfolio of weapons available for deployment during inter-bacterial conflict.

scholarly journals Author response: Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones

2020 ◽  
Author(s):  
Shehryar Ahmad ◽  
Kara K Tsang ◽  
Kartik Sachar ◽  
Dennis Quentin ◽  
Tahmid M Tashin ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Secretion System ◽  
Author Response ◽  
Structural Basis ◽  
Type Vi Secretion System ◽  
Type Vi Secretion

scholarly journals Structure of a bacterial Rhs effector exported by the type VI secretion system

2021 ◽  
Author(s):  
Patrick Guenther ◽  
Dennis Quentin ◽  
Shehryar Ahmad ◽  
Kartik Sachar ◽  
Christos Gatsogiannis ◽  
...  
Keyword(s):  
Bacterial Cell ◽  
Secretion System ◽  
Effector Proteins ◽  
Protein Export ◽  
Spike Protein ◽  
Gram Negative Bacteria ◽  
Structural Elements ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Type Vi Secretion

The type VI secretion system (T6SS) is a widespread protein export apparatus found in Gram-negative bacteria. The majority of T6SSs deliver toxic effector proteins into competitor bacteria. Yet, the structure, function, and activation of many of these effectors remains poorly understood. Here, we present the structures of the T6SS effector RhsA from Pseudomonas protegens and its cognate T6SS spike protein, VgrG1, at 3.3 Å resolution. The structures reveal that the rearrangement hotspot (Rhs) repeats of RhsA assemble into a closed anticlockwise β-barrel spiral similar to that found in bacterial insecticidal Tc toxins and in metazoan teneurin proteins. We find that the C-terminal toxin domain of RhsA is autoproteolytically cleaved but remains inside the Rhs ′cocoon′ where, with the exception of three ordered structural elements, most of the toxin is disordered. The N-terminal ′plug′ domain is unique to T6SS Rhs proteins and resembles a champagne cork that seals the Rhs cocoon at one end while also mediating interactions with VgrG1. Interestingly, this domain is also autoproteolytically cleaved inside the cocoon but remains associated with it. We propose that mechanical force is required to remove the cleaved part of the plug, resulting in the release of the toxin domain as it is delivered into a susceptible bacterial cell by the T6SS.

scholarly journals A family of Type VI secretion system effector proteins that form ion-selective pores

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Giuseppina Mariano ◽  
Katharina Trunk ◽  
David J. Williams ◽  
Laura Monlezun ◽  
Henrik Strahl ◽  
...  
Keyword(s):  
Opportunistic Pathogen ◽  
Effector Proteins ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
New Family ◽  
Type Vi Secretion ◽  
Genes Encoding ◽  
Outer Membrane Permeability ◽  
Bacterial Effectors

AbstractType VI secretion systems (T6SSs) are nanomachines widely used by bacteria to deliver toxic effector proteins directly into neighbouring cells. However, the modes of action of many effectors remain unknown. Here we report that Ssp6, an anti-bacterial effector delivered by a T6SS of the opportunistic pathogen Serratia marcescens, is a toxin that forms ion-selective pores. Ssp6 inhibits bacterial growth by causing depolarisation of the inner membrane in intoxicated cells, together with increased outer membrane permeability. Reconstruction of Ssp6 activity in vitro demonstrates that it forms cation-selective pores. A survey of bacterial genomes reveals that genes encoding Ssp6-like effectors are widespread in Enterobacteriaceae and often linked with T6SS genes. We conclude that Ssp6 and similar proteins represent a new family of T6SS-delivered anti-bacterial effectors.

scholarly journals Crystal structure of the Agrobacterium tumefaciens type VI effector–immunity complex

2018 ◽  
Vol 74 (12) ◽  
pp. 810-816 ◽  
Author(s):  
Satoshi Fukuhara ◽  
Takanori Nakane ◽  
Keitaro Yamashita ◽  
Ryohei Ishii ◽  
Ryuichiro Ishitani ◽  
...  
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Three Dimensional ◽  
Effector Proteins ◽  
Gram Negative Bacteria ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Defense Systems ◽  
Type Vi Secretion ◽  
Inhibitory Mechanisms ◽  
Microbial Defense

The type VI secretion system (T6SS) comprises needle-shaped multisubunit complexes that play a role in the microbial defense systems of Gram-negative bacteria. Some Gram-negative bacteria harboring a T6SS deliver toxic effector proteins into the cytoplasm or periplasm of competing bacteria in order to lyse and kill them. To avoid self-cell disruption, these bacteria have cognate immunity proteins that inhibit their toxic effector proteins. T6SS amidase effector protein 4 (Tae4) and T6SS amidase immunity protein 4 (Tai4) are a representative of the toxic effector–immunity pairs of the T6SS. Here, the three-dimensional structures of Tai4 and the Tae4–Tai4 complex from Agrobacterium tumefaciens are reported at 1.55 and 1.9 Å resolution, respectively. A structural comparison with other Tae4–Tai4 homologs revealed similarities and differences in the catalytic and inhibitory mechanisms among the Tae4 and Tai4 family proteins.

scholarly journals Structure of a bacterial Rhs effector exported by the type VI secretion system

2022 ◽  
Vol 18 (1) ◽  
pp. e1010182
Author(s):  
Patrick Günther ◽  
Dennis Quentin ◽  
Shehryar Ahmad ◽  
Kartik Sachar ◽  
Christos Gatsogiannis ◽  
...  
Keyword(s):  
Bacterial Cell ◽  
Secretion System ◽  
Effector Proteins ◽  
Protein Export ◽  
Spike Protein ◽  
Gram Negative Bacteria ◽  
Structural Elements ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Type Vi Secretion

The type VI secretion system (T6SS) is a widespread protein export apparatus found in Gram-negative bacteria. The majority of T6SSs deliver toxic effector proteins into competitor bacteria. Yet, the structure, function, and activation of many of these effectors remains poorly understood. Here, we present the structures of the T6SS effector RhsA from Pseudomonas protegens and its cognate T6SS spike protein, VgrG1, at 3.3 Å resolution. The structures reveal that the rearrangement hotspot (Rhs) repeats of RhsA assemble into a closed anticlockwise β-barrel spiral similar to that found in bacterial insecticidal Tc toxins and in metazoan teneurin proteins. We find that the C-terminal toxin domain of RhsA is autoproteolytically cleaved but remains inside the Rhs ‘cocoon’ where, with the exception of three ordered structural elements, most of the toxin is disordered. The N-terminal ‘plug’ domain is unique to T6SS Rhs proteins and resembles a champagne cork that seals the Rhs cocoon at one end while also mediating interactions with VgrG1. Interestingly, this domain is also autoproteolytically cleaved inside the cocoon but remains associated with it. We propose that mechanical force is required to remove the cleaved part of the plug, resulting in the release of the toxin domain as it is delivered into a susceptible bacterial cell by the T6SS.

scholarly journals Identification of divergent type VI secretion effectors using a conserved chaperone domain

2015 ◽  
Vol 112 (29) ◽  
pp. 9106-9111 ◽  
Author(s):  
Xiaoye Liang ◽  
Richard Moore ◽  
Mike Wilton ◽  
Megan J. Q. Wong ◽  
Linh Lam ◽  
...  
Keyword(s):  
Functional Characterization ◽  
Large Family ◽  
Effector Proteins ◽  
Gram Negative Bacteria ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Effector Genes ◽  
Type Vi Secretion ◽  
Bacterial Fitness

The type VI secretion system (T6SS) is a lethal weapon used by many bacteria to kill eukaryotic predators or prokaryotic competitors. Killing by the T6SS results from repetitive delivery of toxic effectors. Despite their importance in dictating bacterial fitness, systematic prediction of T6SS effectors remains challenging due to high effector diversity and the absence of a conserved signature sequence. Here, we report a class of T6SS effector chaperone (TEC) proteins that are required for effector delivery through binding to VgrG and effector proteins. The TEC proteins share a highly conserved domain (DUF4123) and are genetically encoded upstream of their cognate effector genes. Using the conserved TEC domain sequence, we identified a large family of TEC genes coupled to putative T6SS effectors in Gram-negative bacteria. We validated this approach by verifying a predicted effector TseC in Aeromonas hydrophila. We show that TseC is a T6SS-secreted antibacterial effector and that the downstream gene tsiC encodes the cognate immunity protein. Further, we demonstrate that TseC secretion requires its cognate TEC protein and an associated VgrG protein. Distinct from previous effector-dependent bioinformatic analyses, our approach using the conserved TEC domain will facilitate the discovery and functional characterization of new T6SS effectors in Gram-negative bacteria.

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