Twin-arginine translocation pathway

{{Short description|Protein export pathway}}

{{Infobox protein family

| Symbol = TatC

| Name = TatC

| image =

| width =

| caption =

| Pfam = PF00902

| Pfam_clan =

| InterPro = IPR002033

| SMART =

| PROSITE =

| MEROPS =

| SCOP =

| TCDB = 2.A.64

| OPM family = 63

| OPM protein = 4b4a

| CAZy =

| CDD =

| Membranome superfamily = 435

}}

{{Infobox protein family

| Symbol = MttA_Hcf106

| Name = TatA/B/E

| image =

| width =

| caption =

| Pfam = PF02416

| Pfam_clan =

| InterPro = IPR003369

| SMART =

| PROSITE =

| MEROPS =

| SCOP =

| TCDB = 2.A.64

| OPM family = 63

| OPM protein = 2l16

| CAZy =

| CDD =

}}

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.{{cite journal

| author = Sargent, F. |author2=Berks, B.C. |author3=Palmer, T.|author-link3=Tracy Palmer

| year = 2006

| title = Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins

| journal = FEMS Microbiol. Lett.

| pmid = 16445746

| volume = 254

| issue = 2

| pages = 198–207

| doi = 10.1111/j.1574-6968.2005.00049.x

| doi-access = free

}} The existence of a Tat translocase in plant mitochondria is also proposed.{{Cite journal|last1=Carrie|first1=Chris|last2=Weißenberger|first2=Stefan|last3=Soll|first3=Jürgen|date=2016-10-15|title=Plant mitochondria contain the protein translocase subunits TatB and TatC|journal=Journal of Cell Science|language=en|volume=129|issue=20|pages=3935–3947|doi=10.1242/jcs.190975|pmid=27609835 |issn=0021-9533|doi-access=free}}{{Cite journal|last1=Bennewitz|first1=Bationa|last2=Sharma|first2=Mayank|last3=Tannert|first3=Franzisca|last4=Klösgen|first4=Ralf Bernd|date=November 2020|title=Dual targeting of TatA points to a chloroplast-like Tat pathway in plant mitochondria|journal=Biochimica et Biophysica Acta (BBA) - Molecular Cell Research|language=en|volume=1867|issue=11|pages=118816|doi=10.1016/j.bbamcr.2020.118816|pmid=32768405 |s2cid=224889980 |doi-access=free}}

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.{{cite journal

| vauthors=Barnett JP, Eijlander RT, Kuipers OP, Robinson C

| year = 2008

| title = A minimal Tat system from a gram-positive organism: a bifunctional TatA subunit participates in discrete TatAC and TatA complexes

| journal = J. Biol. Chem.

| pmid = 18029357

| volume = 283

| issue = 5

| pages = 2534–2542

| doi=10.1074/jbc.M708134200

| doi-access = free

}}

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.{{cite journal

| author = Chaddock, A.M.

|author2=Mant, A. |author3=Karnauchov, I. |author4=Brink, S. |author5=Herrmann, R.G. |author6=Klösgen, R.B. |author7= Robinson, C.

| year = 1995

| title = A new type of signal peptide: central role of a twin-arginine motif in transfer signals for the delta pH-dependent thylakoidal protein translocase.

| journal = EMBO J.

| volume = 14

| issue = 12

| pages = 2715–2722

| pmid = 7796800

| pmc = 398390

|doi=10.1002/j.1460-2075.1995.tb07272.x }} The signal peptide is removed by a signal peptidase after release of the transported protein from the Tat complex.{{cite journal

| author = Frielingsdorf, S.

|author2=Klösgen, R.B.

| year = 2007

| title = Prerequisites for Terminal Processing of Thylakoidal Tat Substrates

| journal = J. Biol. Chem.

| pmid = 17581816

| volume = 282

| issue = 33

| pages = 24455–24462

| doi = 10.1074/jbc.M702630200

| doi-access = free

}} At least two TatC molecules co-exist within each Tat translocon.{{cite journal |vauthors=Sargent F, Bogsch EG, Stanley NR, Wexler M, Robinson C, Berks BC, Palmer T | title = Overlapping functions of components of a bacterial Sec-independent protein export pathway | journal = EMBO Journal | volume = 17 | issue = 13 | pages = 3640–50 |year=1998 | pmid = 9649434 | pmc = 1170700 | doi = 10.1093/emboj/17.13.3640 }}{{cite journal |vauthors=Gouffi K, Santini CL, Wu LF | title = Topology determination and functional analysis of the Escherichia coli TatC protein | journal = FEBS Lett. | volume = 525 | issue = 1–3 | pages = 65–70 |date=August 2002 | pmid = 12163163 | doi = 10.1016/s0014-5793(02)03069-7| doi-access = | bibcode = 2002FEBSL.525...65G }}