Diverse type VI secretion phospholipases are functionally plastic antibacterial effectors (original) (raw)
Related papers
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 EMBO Journal
The bacterial Type VI secretion system (T6SS) is a macromolecular machine that injects effectors into prokaryotic and eukaryotic cells. The mode of action of the T6SS is similar to contractile phages: the contraction of a sheath structure pushes a tube topped by a spike into target cells. Effectors are loaded onto the spike or confined into the tube. In enteroaggregative E. coli, the Tle1 phospholipase binds the C-terminal extension of the VgrG trimeric spike. Here we purify the VgrG-Tle1 complex and show that a VgrG trimer binds three Tle1 monomers and inhibits their activity. Using covalent cross-linking coupled to highresolution mass spectrometry we provide information on the sites of contact and further identify the requirement for a Tle1 N-terminal secretion sequence in complex formation. Finally, we report the 2.6-Å resolution cryo-electron microscopy tri-dimensional structure of the (VgrG) 3-(Tle1) 3 complex revealing how the effector binds its cargo, and how VgrG inhibits Tle1 phospholipase activity. The inhibition of Tle1 phospholipase activity once bound to VgrG suggests that Tle1 dissociation from VgrG is required upon delivery.
Bacterial phospholipase A: structure and function of an integral membrane phospholipase
Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2000
Within the large family of lipolytic enzymes, phospholipases constitute a very diverse subgroup with physiological functions such as digestion and signal transduction. Most phospholipases may associate with membranes at the lipid-water interface. However, in many Gram-negative bacteria, a phospholipase is present which is located integrally in the bacterial outer membrane. This phospholipase (outer membrane phospholipase A or OMPLA) is involved in transport across the bacterial outer membrane and has been implicated in bacterial virulence. OMPLA is calcium dependent and its activity is strictly regulated by reversible dimerisation. Recently the crystal structure of this integral membrane enzyme has been elucidated. In this review, we summarise the implications of these structural data for the understanding of the function and regulation of OMPLA, and discuss a mechanism for phospholipase dependent colicin release in Escherichia coli. ß
Phospholipase A in Gram-negative bacteria and its role in pathogenesis
Microbiology, 2006
Phospholipase A (PLA) is one of the few enzymes present in the outer membrane of Gram-negative bacteria, and is likely to be involved in the membrane disruption processes that occur during host cell invasion. Both secreted and membrane-bound phospholipase A2 activities have been described in bacteria, fungi and protozoa. Recently there have been increasing reports on the involvement of PLA in bacterial invasion and pathogenesis. This review highlights the latest findings on PLA as a virulence factor in Gram-negative bacteria.
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.
2021
Cells steadily adapt their membrane glycerophospholipid (GPL) composition to changing environmental and developmental conditions. While the regulation of membrane homeostasis via GPL synthesis in bacteria has been studied in detail, the mechanisms underlying the controlled degradation of endogenous GPLs remain unknown. Thus far, the function of intracellular phospholipases A (PLAs) in GPL remodeling (Lands cycle) in bacteria is not clearly established. Here, we identified the first cytoplasmic membrane-bound phospholipase A1 (PlaF) from Pseudomonas aeruginosa involved in the Lands cycle. PlaF is an important virulence factor, as the P. aeruginosa ΔplaF mutant showed strongly attenuated virulence in Galleria mellonella and macrophages. We present a 2.0-Å-resolution crystal structure of PlaF, the first structure that reveals homodimerization of a single-pass transmembrane (TM) full-length protein. PlaF dimerization, mediated solely through the intermolecular interactions of TM and jux...
A Widespread Bacterial Type VI Secretion Effector Superfamily Identified Using a Heuristic Approach
Cell Host & Microbe, 2012
Sophisticated mechanisms are employed to facilitate information exchange between interfacing bacteria. A type VI secretion system (T6SS) of Pseudomonas aeruginosa was shown to deliver cell wall-targeting effectors to neighboring cells. However, the generality of bacteriolytic effectors, and moreover, of antibacterial T6S, remained unknown. Using parameters derived from experimentally validated bacterial T6SS effectors and informatics, we identified a phylogenetically disperse superfamily of T6SS-associated peptidoglycan-degrading effectors. The effectors separate into four families composed of peptidoglycan amidase enzymes of differing specificities. Effectors strictly co-occur with cognate immunity proteins, indicating that selfintoxication is a general property of antibacterial T6SSs and effector delivery by the system exerts a strong selective pressure in nature. The presence of antibacterial effectors in a plethora of organisms, including many that inhabit or infect polymicrobial niches in the human body, suggests that the system could mediate interbacterial interactions of both environmental and clinical significance.
Antibacterial actions of secreted phospholipases A2. Review
Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2008
Antibacterial properties of secreted phospholipases A 2 (PLA 2 ) have emerged gradually. Group (G) IIA PLA 2 is the most potent among mammalian secreted (s) PLA 2 s against Gram-positive bacteria, but additional antibacterial compounds, e.g. the bactericidal/permeabilityincreasing protein, are needed to kill Gram-negative bacteria. The mechanisms of binding to the bacterial surface and the killing of bacteria by sPLA 2 s are based on the positive charge of the PLA 2 protein and its phospholipolytic enzymatic activity, respectively. The concentration of GIIA PLA 2 is highly elevated in serum of patients with bacterial sepsis, and overexpression of GIIA PLA 2 protects transgenic mice against experimental Gram-positive infection. The synthesis and secretion of GIIA PLA 2 are stimulated by the cytokines TNF-α, IL-1 and IL-6. Secreted PLA 2 s may be potentially useful new endogenous antibiotics to combat infections including those caused by antibiotic-resistant bacteria such as methicillinresistant staphylococci and vancomysin-resistant enterococci.
Biochimica Et Biophysica Acta-biomembranes, 2010
Antibacterial Lipid phase behavior Gram-positive FTIR As one of its primary physiological functions, sPLA 2 -IIA appears to act as an antibacterial agent. In particular, sPLA 2 -IIA shows high activity towards Gram-positive bacteria such as Staphylococcus aureus (S. aureus). This antibacterial activity results from the preference of the enzyme towards membranes enriched in anionic lipids, which is a common feature of bacterial membranes. An intriguing aspect observed in a variety of bacterial membranes is the presence of a broad but cooperative lipid chain melting event where the lipids in the membrane transition from a solid-ordered (so) into a liquid-disordered (ld) state close to physiological temperatures. It is known that the enzyme is sensitive to the level of lipid packing, which changes sharply between the so and the ld states. Therefore, it would be expected that the enzyme activity is regulated by the bacterial membrane thermotropic behavior. We determine by FTIR the thermotropic lipid chain melting behavior of S. aureus and find that the activity of sPLA 2 -IIA drops sharply in the so state. The activity of the enzyme is also evaluated in terms of its effects on cell viability, showing that cell survival increases when the bacterial membrane is in the so state during enzyme exposure. These results point to a mechanism by which bacteria can develop increased resistance towards antibacterial agents that act on the membrane through a cooperative increase in the order of the lipid chains. These results show that the physical behavior of the bacterial membrane can play an important role in regulating physiological function in an in vivo system.