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The twin-arginine translocation (Tat) pathway serves the role of transporting folded proteins across energy-transducing membranes [1]. Homologs of the genes that encode the transport apparatus occur in archaea, bacteria, chloroplasts, and plant mitochondria [2]. In bacteria, the Tat pathway catalyzes the export of proteins from the cytoplasm across the inner/cytoplasmic membrane. In chloroplasts, the Tat components are found in the thylakoid membrane and direct the import of proteins from the stroma. The Tat pathway acts separately from the general secretory (Sec) pathway, which transports proteins in an unfolded state [3].

It is generally accepted that the primary role of the Tat system is to translocate fully folded proteins across membranes. An example of proteins that need to be exported in their 3D conformation are redox proteins that have acquired complex multiatom cofactors in the bacterial cytoplasm (or the chloroplast stroma or mitochondrial matrix). They include hydrogenases, formate dehydrogenases, nitrate reductases, trimethylamine N-oxide (TMAO) reductases and dimethyl sulfoxide (DMSO) reductases [4,5]. The Tat system can also export whole heteroligomeric complexes in which some proteins have no Tat signal. This is the case of the DMSO reductase or formate dehydrogenase complexes. But there are also other cases where the physiological rationale for targeting a protein to the Tat signal is less obvious. Indeed, there are examples of homologous proteins that are in some cases targeted to the Tat pathway and in other cases to the Sec apparatus. Some examples are: copper nitrite reductases, flavin domains of flavocytochrome c and N-acetylmuramoyl-L-alanine amidases [6].

In halophilic archaea such as Halobacterium almost all secreted proteins appear to be Tat targeted. It has been proposed to be a response to the difficulties these organisms would otherwise face in successfully folding proteins extracellularly at high ionic strength [7].

The Tat signal peptide consists of three motifs: the positively charged N-terminal motif, the hydrophobic region and the C-terminal region that generally ends with a consensus short motif (A-x-A) specifying cleavage by signal peptidase. Sequence analysis revealed that signal peptides capable of targeting the Tat protein contain the consensus sequence [ST]-R-R-x-F-L-K. The nearly invariant twin-arginine gave rise to the pathway's name. In addition the h-region of Tat signal peptides is typically less hydrophobic than that of Sec-specific signal peptides [4,5].

The profile we developed recognizes the whole prokaryotic and archeal Tat signal from the methionine to the A-x-A short motif.

May 2007 / First entry.

PROSITE method (with tools and information) covered by this documentation:

TAT, PS51318; Twin arginine translocation (Tat) signal profile  (MATRIX)

Sequences known to belong to this class detected by the profile: ALL, except for 5 proteins Other sequence(s) detected in Swiss-Prot: 5

• Domain architecture view of Swiss-Prot proteins matching PS51318 • Retrieve an alignment of Swiss-Prot true positive hits:   Clustal format, color, condensed view  / Clustal format, color  / Clustal format, plain text  / Fasta format • Retrieve the sequence logo from the alignment • Taxonomic tree view of all Swiss-Prot/TrEMBL entries matching PS51318 • Retrieve a list of all Swiss-Prot/TrEMBL entries matching PS51318 • Scan Swiss-Prot/TrEMBL entries against PS51318 • view ligand binding statistics

Matching PDB structures: 2PQ4 [ALL]

1	Authors	Wickner W., Schekman R.
	Title	Protein translocation across biological membranes.
	Source	Science 310:1452-1456(2005).
	PubMed ID	16322447
	DOI	10.1126/science.1113752

2	Authors	Yen M.R., Tseng Y.H., Nguyen E.H., Wu L.F., Saier M.H. Jr.
	Title	Sequence and phylogenetic analyses of the twin-arginine targeting (Tat) protein export system.
	Source	Arch. Microbiol. 177:441-450(2002).
	PubMed ID	12029389
	DOI	10.1007/s00203-002-0408-4

3	Authors	Stephenson K.
	Title	Sec-dependent protein translocation across biological membranes: evolutionary conservation of an essential protein transport pathway (review).
	Source	Mol. Membr. Biol. 22:17-28(2005).
	PubMed ID	16092521

4	Authors	Lee P.A., Tullman-Ercek D., Georgiou G.
	Title	The bacterial twin-arginine translocation pathway.
	Source	Annu. Rev. Microbiol. 60:373-395(2006).
	PubMed ID	16756481
	DOI	10.1146/annurev.micro.60.080805.142212

5	Authors	Robinson C., Bolhuis A.
	Title	Tat-dependent protein targeting in prokaryotes and chloroplasts.
	Source	Biochim. Biophys. Acta 1694:135-147(2004).
	PubMed ID	15546663
	DOI	10.1016/j.bbamcr.2004.03.010

6	Authors	Berks B.C., Palmer T., Sargent F.
	Title	Protein targeting by the bacterial twin-arginine translocation (Tat) pathway.
	Source	Curr. Opin. Microbiol. 8:174-181(2005).
	PubMed ID	15802249
	DOI	10.1016/j.mib.2005.02.010

7	Authors	Bolhuis A.
	Title	Protein transport in the halophilic archaeon Halobacterium sp. NRC-1: a major role for the twin-arginine translocation pathway?
	Source	Microbiology 148:3335-3346(2002).
	PubMed ID	12427925

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