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Mol Microbiol. 2016 Mar;99(6):1099-118. doi: 10.1111/mmi.13292. Epub 2016 Feb 10.

A phospholipase A1 antibacterial Type VI secretion effector interacts directly with the C-terminal domain of the VgrG spike protein for delivery.

Author information

1
Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS - Aix-Marseille Université, UMR 7255, Institut de Microbiologie de la Méditerranée, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
2
Architecture et Fonction des Macromolécules Biologiques, CNRS - UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France.
3
Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France.
4
Laboratoire d'Enzymologie Interfaciale et de Physiologie de la Lipolyse, CNRS - Aix-Marseille Université, UMR 7282, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.

Abstract

The Type VI secretion system (T6SS) is a multiprotein 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 towards 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 interbacterial 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 demonstrate that the C-terminal extension domain of VgrG1, including a transthyretin-like domain, is responsible for the interaction with Tle1 and its subsequent delivery into target cells. Based on these results, we propose an additional mechanism of transport of T6SS effectors in which cognate effectors are selected by specific motifs located at the C-terminus of VgrG proteins.

PMID:
26714038
DOI:
10.1111/mmi.13292
[Indexed for MEDLINE]
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