Twin-arginine translocation (Tat) pathway

The twin-arginine translocation, or Tat, pathway is a protein export, or secretion pathway found in plants, bacteria, and archaea. It serves to actively translocate folded proteins across a lipid membrane bilayer. In plants, the Tat translocase is found in the thylakoid membrane of the chloroplast, where it acts to import proteins into the thylakoid lumen. In bacteria, the Tat translocase is found in the cytoplasmic membrane and serves to export proteins to the cell envelope, or to the extracellular space [1].

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The Tat translocase is composed of the membrane proteins TatA, TatB, and TatC. In Escherichia coli, a fourth gene, tatE encodes a functionally redundant TatA protein.

The Tat pathway in pathogens

Not all bacteria carry the tatABC genes in their genome[2]; however, of those that do, there seems to be no discrimination between pathogens and nonpathogens. Despite that fact, some pathogenic bacteria such as Pseudomonas aeruginosa, Legionella pneumophila, Yersinia pseudotuberculosis, and E. coli O157:H7 rely on a functioning Tat pathway for full virulence in infection models. In addition, a number of exported virulence factors have been shown to rely on the Tat pathway. One such category of virulence factors are the phospholipase C enzymes, which have been shown to be Tat-exported in Pseudomonas aeruginosa, and thought to be Tat-exported in Mycobacterium tuberculosis.

References

[1] Sargent et al., "Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins" FEMS Microbiol Lett, 254 (2):198-207