Manipulating the type VI secretion system spike to shuttle passenger proteins (original) (raw)
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Frontiers in Microbiology
The bacterial pathogen Pseudomonas aeruginosa uses three type VI secretion systems (T6SSs) to drive a multitude of effector proteins into eukaryotic or prokaryotic target cells. The T6SS is a supramolecular nanomachine, involving a set of 13 core proteins, which resembles the contractile tail of bacteriophages and whose tip is considered as a puncturing device helping to cross membranes. Effectors can attach directly to the T6SS spike which is composed of a VgrG (valine-glycine-rich proteins) trimer, of which P. aeruginosa produces several. We have previously shown that the master regulator RsmA controls the expression of all three T6SS gene clusters (H1-, H2-and H3-T6SS) and a range of remote vgrG and effector genes. We also demonstrated that specific interactions between VgrGs and various T6SS effectors are prerequisite for effector delivery in a process we called "à la carte delivery." Here, we provide an indepth description on how the two H2-T6SS-dependent effectors PldA and PldB are delivered via their cognate VgrGs, VgrG4b and VgrG5, respectively. We show that specific recognition of the VgrG C terminus is required and effector specificity can be swapped by exchanging these C-terminal domains. Importantly, we established that effector recognition by a cognate VgrG is not always sufficient to achieve successful secretion, but it is crucial to provide effector stability. This study highlights the complexity of effector adaptation to the T6SS nanomachine and shows how the VgrG tip can possibly be manipulated to achieve effector delivery.
Molecular microbiology, 2015
The Type VI secretion system (T6SS) is a multi-protein machine that delivers protein effectors in both prokaryotic and eukaryotic cells, allowing interbacterial competition and virulence. The mechanism of action of the T6SS requires the contraction of a sheath-like structure that propels a needle toward target cells, allowing the delivery of protein effectors. Here, we provide evidence that the entero-aggregative Escherichia coli Sci-1 T6SS is required to eliminate competitor bacteria. We further identify Tle1, a toxin effector encoded by this cluster and showed that Tle1 possesses phospholipase A1 and A2 activities required for the inter-bacterial competition. Self-protection of the attacker cell is secured by an outer membrane lipoprotein, Tli1, which binds Tle1 in a 1:1 stoichiometric ratio with nanomolar affinity, and inhibits its phospholipase activity. Tle1 is delivered into the periplasm of the prey cells using the VgrG1 needle spike protein as carrier. Further analyses demon...
The rise of the Type VI secretion system
F1000prime reports, 2013
Bacterial cells have developed multiple strategies to communicate with their surrounding environment. The intracellular compartment is separated from the milieu by a relatively impermeable cell envelope through which small molecules can passively diffuse, while larger macromolecules, such as proteins, can be actively transported. In Gram-negative bacteria, the cell envelope is a double membrane, which houses several supramolecular protein complexes that facilitate the trafficking of molecules. For example, bacterial pathogens use these types of machines to deliver toxins into target eukaryotic host cells, thus subverting host cellular functions. Six different types of nanomachines, called Type I - Type VI secretion systems (T1SS - T6SS), can be readily identified by their composition and mode of action. A remarkable feature of these protein secretion systems is their similarity to systems with other biological functions, such as motility or the exchange of genetic material. The T6SS...
The VgrG proteins are "A la carte" delivery systems for bacterial type VI effectors
Journal of Biological Chemistry, 2014
The type VI secretion system (T6SS) is involved in bacterial warfare. Results: Novel H1-T6SS-dependent toxins from Pseudomonas aeruginosa are identified using an in vitro bacterial killing assay. Conclusion: The newly identified toxins showed a requirement for specific VgrG proteins. Significance: VgrG proteins may represent an independent form of T6SS-dependent secretion, resembling the contact-dependent growth inhibition (CDI) system.
bioRxiv (Cold Spring Harbor Laboratory), 2021
The type six secretion system (T6SS) is a prevalent bacterial weapon delivering toxic effector proteins into nearby competitors. In addition to immunity genes that protect against a particular effector, alternate yet crucial nonspecific defences have also recently been identified. To systematically identify genes influencing T6SS susceptibility in numerous species, we designed a Tn-Seq-based competition assay. Combined with follow-up analyses using E. coli and V. cholerae gene knockout collections, we demonstrate that our Tn-Seq competition technique can be used to identify both immunity and non-immunity defences against the T6SS. We also identify E. coli proteins that facilitate T6SS-mediated cell death, including metabolic genes such as cyaA and gltA, where mutant strains were resistant to attack. Our findings act as a proof-of-concept for the technique while also illuminating novel genes of interest. Since Tn-Seq can be applied in numerous species, our method has broad potential for identifying diverse T6SS defence genes across genomes in a high-throughput manner. Importance The type six secretion system (T6SS) is a molecular poison-tipped spear that bacteria use to kill nearby competitors. To prevent self killing, they use antitoxins called immunity genes that specifically neutralize the poisons. Beyond immunity genes, multiple additional defences have recently been discovered but there are likely many more across the genomes of diverse species. To help discover these novel mechanisms, we designed a high-throughput method that can be used in numerous different species to rapidly identify genes involved in sensitivity to T6SS attacks. Using T6SS 'killers' delivering individual poisons and two commonly studied 'prey' bacteria, we show proof-of-principle that the technique can discover proteins that make the prey cells more resistant or sensitive to particular. CC-BY-NC-ND 4.
The Versatile Type VI Secretion System
Microbiology Spectrum
Bacterial type VI secretion systems (T6SSs) function as contractile nanomachines to puncture target cells and deliver lethal effectors. In the 10 years since the discovery of the T6SS, much has been learned about the structure and function of this versatile protein secretion apparatus. Most of the conserved protein components that comprise the T6SS apparatus itself have been identified and ascribed specific functions. In addition, numerous effector proteins that are translocated by the T6SS have been identified and characterized. These protein effectors usually represent toxic cargoes that are delivered by the attacker cell to a target cell. Researchers in the field are beginning to better understand the lifestyle or physiology that dictates when bacteria normally express their T6SS. In this article, we consider what is known about the structure and regulation of the T6SS, the numerous classes of antibacterial effector T6SS substrates, and how the action of the T6SS relates to a giv...
Cancer therapy can be limited by potential side effects, and bacteria-based living cancer therapeutics have gained scientific interest in recent years. However, the full potential of bacteria as therapeutics has yet to be explored due to engineering challenges. n this study, we present a bacterial device designed to specifically target and eliminate breast cancer cells. We have engineeredEscherichia coli(E. coli) to secrete a Shiga toxin, HlyE, which is a pore-forming protein that binds to HER2 receptors on breast cancer cells. This binding is facilitated by a nanobody expressed on the bacteria’s surface via the Ag43 autotransporter protein system. Our findings demonstrate that the nanobody efficiently binds to HER2+ cells in vitro, and we have utilized the YebF secretion system to secrete HlyE and kill the target cancer cells. Overall, our results highlight the potential of our engineered bacteria as an innovative strategy for breast cancer treatment.
A Type VI Secretion System of Pseudomonas aeruginosa Targets a Toxin to Bacteria
Cell Host & Microbe, 2010
The functional spectrum of a secretion system is defined by its substrates. Here we analyzed the secretomes of Pseudomonas aeruginosa mutants altered in regulation of the Hcp Secretion Island-I-encoded type VI secretion system (H1-T6SS). We identified three substrates of this system, proteins Tse1–3 (type six exported 1–3), which are coregulated with the secretory apparatus and secreted under tight posttranslational control. The Tse2 protein was found to be the toxin component of a toxin-immunity system and to arrest the growth of prokaryotic and eukaryotic cells when expressed intracellularly. In contrast, secreted Tse2 had no effect on eukaryotic cells; however, it provided a major growth advantage for P. aeruginosa strains, relative to those lacking immunity, in a manner dependent on cell contact and the H1-T6SS. This demonstration that the T6SS targets a toxin to bacteria helps reconcile the structural and evolutionary relationship between the T6SS and the bacteriophage tail and spike.► The HSI-I-encoded T6SS of P. aeruginosa secretes three proteins, Tse1–3 ► Tse2 is a toxin capable of acting on prokaryotic and eukaryotic cells ► Tsi2 is an essential gene that provides immunity to Tse2 ► The HSI-I-encoded T6SS targets Tse2 to bacterial, not eukaryotic, cells