A type VI secretion system effector delivery mechanism dependent on PAAR and a chaperone–co-chaperone complex

Abstract

The type VI secretion system (T6SS) is used by many Gram-negative bacteria as a molecular weapon to modulate neighbouring bacterial and eukaryotic cells, thereby affecting the dynamics of community structure in multiple species environments. The T6SS injects its inner-needle Hcp tube, the sharpening tip complex consisting of VgrG and PAAR, and toxic effectors into neighbouring cells. Its functions are largely determined by the activities of its delivered effectors. Six mechanisms of effector delivery have been described: two mediated by the inner tube and the others mediated by the VgrG and PAAR tip complex. Here, we report an additional effector delivery mechanism that relies on interaction with a chaperone complex and a PAAR protein as a carrier. The Pseudomonas aeruginosa PAO1 TOX-REase-5 domain-containing effector TseT directly interacts with PAAR4 and the chaperone TecT for delivery, and an immunity protein, TsiT, for protection from its toxicity. TecT forms a complex with its co-chaperone, co-TecT, which is disrupted by the carboxy-terminal tail of PAAR4. In addition, we delineate a complex, multilayered competitive process that dictates effector trafficking. PAAR delivery provides an additional tool for engineering cargo protein translocation.

Diversity of phytobeneficial traits revealed by whole‐genome analysis of worldwide‐isolated phenazine‐producing Pseudomonas spp.

“…Recently, Burkinshaw et al, described a similar cluster in P. aeruginosa PAO1. They found that TseT, a TOX‐REase‐5 domain‐containing effector, directly interacts with PAAR and the DUF4123 domain‐containing protein for its delivery through the H2‐T6SS (Burkinshaw et al, ). We also found genes encoding predicted triglyceride lipases nearby orphan vgrG genes in most genomes and genes encoding predicted phospholipase D within H2‐T6SS clusters in strains from the P. chlororaphis subgroup (Fig.…”

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

“…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.…”

“…2). The VgrG and PAAR are known to be encoded in some but not all T6SS apparatus encoding gene clusters 23,32,33 .As shown in Fig 1a, the T6SS-2 gene cluster encodes a VgrG protein but lacks PAAR protein, while the T6SS-1 cluster lacks both VgrG and PAAR. Considering this, we hypothesized that effectors which have VgrG (VgrG effector ) encoded in the same operon might be secreted through T6SS-1 while those which are not co-encoded with VgrG would perforce have to be secreted through T6SS-2 (Fig.…”

“…Association with HCP/VgrG/PAAR proteins/domains is essential for translocation of effectors. Recent studies have suggested that certain chaperone (DUF4123, DUF1795 and DUF2169) and co-chaperones are also required for T6SS mediated delivery of effectors 20–23 . Till date, diverse kinds of proteins including phospholipases (Tli), amidases (Tae), glucosaminidase (Tge), nucleases (Rhs proteins), DNases (Tde), peptidases, pore-forming toxins etc.…”

“…have been identified as T6SS effectors from different bacteria 24–26 . These effectors demonstrate potent bactericidal activity by targeting the DNA/RNA/cell wall components of the prey bacterium 23–25 . However to protect self as well as sister cells from intoxication, bacteria have evolved cognate immunity proteins against each T6SS effector 25,27,28 .…”