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Twin-arginine translocation pathway

The twin-arginine translocation pathway (Tat pathway) is a protein export, or secretion pathway found in plants, bacteria, and archaea. In contrast to the Sec pathway which transports proteins in an unfolded manner, the Tat pathway serves to actively translocate folded proteins across a lipid membrane bilayer. In plants, the Tat translocase is located in the thylakoid membrane of the chloroplast, where it acts to export 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]

TatC
Identifiers
SymbolTatC
PfamPF00902
InterProIPR002033
TCDB2.A.64
OPM superfamily63
OPM protein4b4a
Membranome435
TatA/B/E
Identifiers
SymbolMttA_Hcf106
PfamPF02416
InterProIPR003369
TCDB2.A.64
OPM superfamily63
OPM protein2l16

In the plant thylakoid membrane and in Gram-negative bacteria the Tat translocase is composed of three essential membrane proteins; TatA, TatB, and TatC. In the most widely studied Tat pathway, that of the Gram-negative bacterium Escherichia coli, these three proteins are expressed from an operon with a fourth Tat protein, TatD, which is not required for Tat function. A fifth Tat protein TatE that is homologous to the TatA protein is present at a much lower level in the cell than TatA and is not believed to play any significant role in Tat function.

The Tat pathways of Gram-positive bacteria differ in that they do not have a TatB component. In these bacteria the Tat system is made up from a single TatA and TatC component, with the TatA protein being bifunctional and fulfilling the roles of both E. coli TatA and TatB.[2]

The name of the Tat pathway relates to a highly conserved twin-arginine leader motif (S/TRRXFLK) which is found in the N terminal Signal peptide of the corresponding passenger proteins.[3] The signal peptide is removed by a signal peptidase after release of the transported protein from the Tat complex.[4] At least two TatC molecules co-exist within each Tat translocon.[5][6]

In pathogensEdit

Not all bacteria carry the tatABC genes in their genome;[7] 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.

ReferencesEdit

  1. ^ Sargent, F.; Berks, B.C.; Palmer, T. (2006). "Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins". FEMS Microbiol. Lett. 254 (2): 198–207. doi:10.1111/j.1574-6968.2005.00049.x. PMID 16445746.
  2. ^ Barnett JP, Eijlander RT, Kuipers OP, Robinson C (2008). "A minimal Tat system from a gram-positive organism: a bifunctional TatA subunit participates in discrete TatAC and TatA complexes". J. Biol. Chem. 283 (5): 2534–2542. doi:10.1074/jbc.M708134200. PMID 18029357.
  3. ^ Chaddock, A.M.; Mant, A.; Karnauchov, I.; Brink, S.; Herrmann, R.G.; Klösgen, R.B.; Robinson, C. (1995). "A new type of signal peptide: central role of a twin-arginine motif in transfer signals for the delta pH-dependent thylakoidal protein translocase". EMBO J. 14 (12): 2715–2722. doi:10.1002/j.1460-2075.1995.tb07272.x. PMC 398390. PMID 7796800.
  4. ^ Frielingsdorf, S.; Klösgen, R.B. (2007). "Prerequisites for Terminal Processing of Thylakoidal Tat Substrates". J. Biol. Chem. 282 (33): 24455–24462. doi:10.1074/jbc.M702630200. PMID 17581816.
  5. ^ Sargent F, Bogsch EG, Stanley NR, Wexler M, Robinson C, Berks BC, Palmer T (1998). "Overlapping functions of components of a bacterial Sec-independent protein export pathway". EMBO Journal. 17 (13): 3640–50. doi:10.1093/emboj/17.13.3640. PMC 1170700. PMID 9649434.
  6. ^ Gouffi K, Santini CL, Wu LF (August 2002). "Topology determination and functional analysis of the Escherichia coli TatC protein". FEBS Lett. 525 (1–3): 65–70. doi:10.1016/s0014-5793(02)03069-7. PMID 12163163.
  7. ^ Organism