PAAR proteins act as the ‘sorting hat’ of the type VI secretion system

Wood, Thomas E.; Howard, Sophie A.; Wettstadt, Sarah; Filloux, Alain

doi:10.1099/mic.0.000842

Cited by 46 publications

(39 citation statements)

References 49 publications

(82 reference statements)

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“…the presence of two long helices followed by the DUF2345 and the TTR domains) corresponds to the COG4532 found at the C-terminal domain of a subgroup of VgrG proteins in Proteobacteria (Boyer et al, 2009). This group includes proteins such as the VgrG encoded upstream of a putative Tle3 effector in uropathogenic E. coli CFT073, or VgrG2a from P. aeruginosa encoded upstream the Tle4-like tlpE effector (Wood et al, 2019; Appendix Fig S7). The structural organization of these VgrG proteins and their genetic link to phospholipaseencoding genes suggest that these phospholipases might also be directly recruited to the spike extension for delivery.…”

Section: A New Mode Of T6ss Substrate Loadingmentioning

confidence: 99%

Structural basis for loading and inhibition of a bacterial T6 SS phospholipase effector by the VgrG spike

et al. 2020

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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 Escherichia 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 high-resolution 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.

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Section: A New Mode Of T6ss Substrate Loadingmentioning

confidence: 99%

Structural basis for loading and inhibition of a bacterial T6 SS phospholipase effector by the VgrG spike

et al. 2020

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“…Additionally, genes residing immediately upstream of t0731 and t0735 homologs contain conserved PAAR and VgrG domains respectively with a C-terminal extension of unknown function. This arrangement is characteristic of ‘evolved PAAR’ and ‘evolved VgrG’, well-known classes of T6SS effector proteins in which a C-terminal effector domain is fused to an expelled component of the T6SS spike as an effector delivery mechanism [ 53 , 54 ]. In a separate instance, we identified a gene residing upstream of a t0735 homolog identified by HMM searches as related to E. coli MepA, which exhibits a peptidoglycan endopeptidase activity shared by established T6SS effectors [ 55 ].…”

Section: Resultsmentioning

confidence: 99%

Identification of A Putative T6SS Immunity Islet in Salmonella Typhi

Barretto¹,

Fowler²

2020

Pathogens

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Typhoid fever is a major global health problem and is the result of systemic infections caused by the human-adapted bacterial pathogen Salmonella enterica serovar Typhi (S. Typhi). The pathology underlying S. Typhi infections significantly differ from infections caused by broad host range serovars of the same species, which are a common cause of gastroenteritis. Accordingly, identifying S. Typhi genetic factors that impart functionality absent from broad host range serovars offers insights into its unique biology. Here, we used an in-silico approach to explore the function of an uncharacterized 14-gene S. Typhi genomic islet. Our results indicated that this islet was specific to the S. enterica species, where it was encoded by the Typhi and Paratyphi A serovars, but was generally absent from non-typhoidal serovars. Evidence was gathered using comparative genomics and sequence analysis tools, and indicated that this islet was comprised of Type VI secretion system (T6SS) and contact-dependent growth inhibition (CDI) genes, the majority of which appeared to encode orphan immunity proteins that protected against the activities of effectors and toxins absent from the S. Typhi genome. We herein propose that this islet represents an immune system that protects S. Typhi against competing bacteria within the human gut.

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“…The VgrG and PAAR proteins play important roles in secretion of T6SS effectors 13,14,16,23 . In NGJ1, we observed either VgrG or PAAR are encoded in the upstream region of various effector operons, indicating that they might act as a carrier for their T6SS mediated delivery (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…A trimer of the VgrG (Valine-glycine repeat protein G) protein forms a spike like structure on the top of the inner tube 12 . Further, the PAAR (proline-alanine-alanine-arginine) repeat-containing protein binds to the distal end of the spike and forms a sharp pointed tip 13,14 . Contraction of the sheath enables the HCP-VgrG-PAAR protein complex to puncture the bacterial membrane and deliver various T6SS effectors into the extracellular environment or directly into the target bacterial cells 8,15,16 .…”

Section: Introductionmentioning

confidence: 99%

Conversion of a defensive toxin-antitoxin system into an offensive T6SS effector in Burkholderia

Yadav

Magotra

Krishnan

et al. 2019

Preprint

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12Bacteria use various kinds of toxins to either inhibit the growth of co-habiting bacteria 13 or when needed control their own growth. Here we report that Burkholderia and 14 certain other bacteria have altered the potential defensive function of Tox-REase-5 15 domain containing toxins into offensive function. The Burkholderia gladioli strain 16 NGJ1 encodes such toxins as type VI secretion system (T6SS) effectors (Tse) and 17 potentially deploys them to kill co-habiting rice endophytic bacteria. Notably, the 18 immunity (Tsi) proteins associated with Tse effectors demonstrate functional 19 similarity with the antitoxin of type II toxin-antitoxin (TA) system. Genome analysis of 20 diverse bacteria revealed that various Tse orthologs are either encoded as TA or 21 T6SS effectors. In addition, potential evolutionary events associated with conversion 22 of TA into T6SS effectors have been delineated. Our results indicate that the 23 transposition of IS3 elements has led to the operonic fusion of certain T6SS related 24 genes with TA genes resulting in their conversion into T6SS effectors. Such a 25 genetic change has enabled bacteria to utilize novel toxins to precisely target co-26 habiting bacteria. 27 28 29Under natural conditions, bacteria have to compete with co-habiting bacteria for 30 available resources. This can lead to severe evolutionary pressure on bacteria to 31 adopt strategies to limit the growth of other cohabiting microbes 1 . Several bacterial 32 species use a specialized protein secretion system called the type VI secretion 33 system (T6SS) to target co-habiting bacteria 2-6 . The T6SS is a syringe like apparatus 34 composed of a base plate, a membrane complex (spanning the inner and outer 35 membrane) and an inner tube, being wrapped in a sheath-like structure 7-10 . 36Hexamers of the HCP (hemolysin-coregulated protein) protein forms the inner tube 37 of the T6SS apparatus 9,11 . A trimer of the VgrG (Valine-glycine repeat protein G) 38 protein forms a spike like structure on the top of the inner tube 12 . Further, the 39 PAAR (proline-alanine-alanine-arginine) repeat-containing protein binds to the 40 distal end of the spike and forms a sharp pointed tip 13,14 . Contraction of the sheath 41 enables the HCP-VgrG-PAAR protein complex to puncture the bacterial 42 membrane and deliver various T6SS effectors into the extracellular environment or 43 directly into the target bacterial cells 8,15,16 . The effectors can be encoded either as 44 fused protein with the HCP/VgrG/PAAR proteins as an additional domain or they 45 are non-covalently fused to HCP/VgrG/PAAR protein that are encoded as 46 upstream ORF in the effector operon 12,15,17-20 . Association with HCP/VgrG/PAAR 47 proteins/domains is essential for translocation of effectors. Recent studies have 48 suggested that certain chaperone (DUF4123, DUF1795 and DUF2169) and co-49 chaperones are also required for T6SS mediated delivery of effectors 20-23 . Till date, 50 diverse kinds of proteins including phospholipases (Tli), amidases (Tae), 51 gl...

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PAAR proteins act as the ‘sorting hat’ of the type VI secretion system

Cited by 46 publications

References 49 publications

Structural basis for loading and inhibition of a bacterial T6 SS phospholipase effector by the VgrG spike

Structural basis for loading and inhibition of a bacterial T6 SS phospholipase effector by the VgrG spike

Identification of A Putative T6SS Immunity Islet in Salmonella Typhi

Conversion of a defensive toxin-antitoxin system into an offensive T6SS effector in Burkholderia

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