The type VI secretion system: translocation of effectors and effector-domains

Por Secretion System of Porphyromonas gingivalis

“…The type secretion system was recently identified and its mechanism has not yet been elucidated. The type secretion system is usually encoded by a cluster of 12 25 genes within a pathogenicity island in Gram negative bacteria, such as Pseudomonas aeruginosa and Salmonella typhimurium 4 . The function and characterization of the components of the type system remain to be elucidated.…”

Type VI Secretion System-Associated Gene Clusters Contribute to Pathogenesis of Salmonella enterica Serovar Typhimurium

“…T6SSs employ the proteins encoded by these genes to coordinate the secretion of protein substrates via the assembly, contraction, and disassembly of a phage-like tail (1,43). For some T6SS-harboring organisms, the core gene encoding the tailspike protein encodes a fusion protein that allows the translocation of an effector domain (43).…”

“…However, in S. Typhimurium and other T6SS-harboring organisms, no evolved tailspike protein is present (5). In addition to the core genes, organisms that possess a T6SS typically encode less-well-conserved, T6SS-associated genes that differ extensively in their number and location throughout the genome, and some of these genes have been reported to act as effector or regulatory proteins (2,14,43). Recently, a set of genes encoding T6SS-secreted toxin proteins were identified in Pseudomonas aeruginosa that are involved in interbacterial competition (45).…”

“…In V. cholerae, some strains constitutively express T6SS-associated proteins while others do not, suggesting niche adaptation (43). Regulatory control at the transcriptional level by the activator of alternative sigma factor 54, VasH, has been observed to occur in V. cholerae (23).…”

“…The expression of these proteins in some organisms is absent under experimental conditions, likely due to the absence of inducing stimuli. This can be circumvented by the use of strains with constitutive T6SS activity, as in the case of a retS mutant of P. syringae or the V52 V. cholerae strain (43,44). Whether or not stable expression and secretion of the Hcp and VrgS proteins occur under in vitro or in vivo conditions in S. Typhimurium is unknown.…”