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J Biol Chem. 2014 Jun 20;289(25):17872-84. doi: 10.1074/jbc.M114.563429. Epub 2014 May 2.

The VgrG proteins are "à la carte" delivery systems for bacterial type VI effectors.

Author information

1
From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
2
From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom a.filloux@imperial.ac.uk.

Abstract

The bacterial type VI secretion system (T6SS) is a supra-molecular complex akin to bacteriophage tails, with VgrG proteins acting as a puncturing device. The Pseudomonas aeruginosa H1-T6SS has been extensively characterized. It is involved in bacterial killing and in the delivery of three toxins, Tse1-3. Here, we demonstrate the independent contribution of the three H1-T6SS co-regulated vgrG genes, vgrG1abc, to bacterial killing. A putative toxin is encoded in the vicinity of each vgrG gene, supporting the concept of specific VgrG/toxin couples. In this respect, VgrG1c is involved in the delivery of an Rhs protein, RhsP1. The RhsP1 C terminus carries a toxic activity, from which the producing bacterium is protected by a cognate immunity. Similarly, VgrG1a-dependent toxicity is associated with the PA0093 gene encoding a two-domain protein with a putative toxin domain (Toxin_61) at the C terminus. Finally, VgrG1b-dependent killing is detectable upon complementation of a triple vgrG1abc mutant. The VgrG1b-dependent killing is mediated by PA0099, which presents the characteristics of the superfamily nuclease 2 toxin members. Overall, these data develop the concept that VgrGs are indispensable components for the specific delivery of effectors. Several additional vgrG genes are encoded on the P. aeruginosa genome and are not linked genetically to other T6SS genes. A closer inspection of these clusters reveals that they also encode putative toxins. Overall, these associations further support the notion of an original form of secretion system, in which VgrG acts as the carrier.

KEYWORDS:

Bacterial Cell Envelope; Bacterial Genetics; Bacterial Toxin; Microbiology; Protein Translocation; Pseudomonas aeruginosa (P. aeruginosa); Type VI Secretion System; VgrG

PMID:
24794869
PMCID:
PMC4067218
DOI:
10.1074/jbc.M114.563429
[Indexed for MEDLINE]
Free PMC Article

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