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Protein targeting by the twin-arginine translocation pathway

Nature Reviews Molecular Cell Biology volume 2, pages 350–356 (2001)Cite this article

Key Points

  • The twin-arginine translocase (Tat) system operates in the chloroplast thylakoid membrane and the plasma membranes of most bacteria.

  • It recognizes substrates that bear signal peptides containing a twin-arginine motif before a hydrophobic region.

  • It is driven, at least in thylakoids, by the proton gradient across the membrane; nucleoside triphosphate hydrolysis is not required.

  • The Tat system is, at present, unique in that it can transport fully folded proteins across tightly sealed membranes.

  • Its substrates include globular proteins that must bind certain cofactors before transport, as well as proteins that seem to fold too quickly/tightly for 'conventional' Sec-type systems to handle.

  • Three genes have been shown to encode important Tat components in Escherichia coli, namely tatA, tatB and tatC.

  • The isolated Tat complex is about 600 kDa but has yet to be analysed in an active state.

Abstract

The twin-arginine translocation pathway operates in the thylakoid membrane of chloroplasts and in the plasma membrane of most free-living bacteria. Its main function is to transport fully folded proteins across the membrane. Three important tat genes have been identified and the sequences of the encoded proteins, together with the unusual properties of the pathway, indicate that the Tat system is completely different from other protein translocases.

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Figure 1: Pathways for protein targeting into thylakoids.
Figure 2: Genes and proteins involved in the Tat pathway in Escherichia coli .
Figure 3: Capabilities of the Tat pathway in Escherichia coli: the export of green fluorescent protein in an active form.
Figure 4: Protein export pathways in bacteria.
Figure 5: The scale of the problem: export of TMAO reductase in a folded form.

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Author information

Authors and Affiliations

  1. Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, United Kingdom

    Colin Robinson & Albert Bolhuis

Authors
  1. Colin Robinson
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Supplementary information

Related links

Related links

DATABASE LINKS

SecA

SecY

SecE

23K

16K

hcf106

four-gene tat operon

tatE

TMAO reductase

FURTHER INFORMATION

Department of Biological Sciences at Warwick University

ENCYCLOPEDIA OF LIFE SCIENCES

Protein translocation across membranes

Bacterial cytoplasmic membrane

Glossary

THYLAKOID

Sac-like vesicle that contains the photosynthetic pigments in photosynthetic organisms.

OXYGEN-EVOLVING COMPLEX

Extrinsic group of photosystem II proteins, bound to the lumenal face of the thylakoid membrane.

OPERON

A unit of genes in prokaryotes that is expressed as a single messenger RNA.

MONOCISTRONIC

Encoding a single polypeptide or protein.

PERIPLASM

Area between the inner and outer membranes of Gram-negative bacteria.

DIHYDROFOLATE REDUCTASE

Enzyme that catalyses the reduction of different forms of hydrofolate. These reduction reactions are linked to the reduction/oxidation of NAD+/NADH.

GREEN FLUORESCENT PROTEIN

(GFP). Autofluorescent protein, originally identified in the jellyfish Aequorea victoria.

POLYPHENOL OXIDASE

Family of copper-containing oxidoreductases that catalyse the oxidation of mono- and o-diphenols to o-diquinones. Found in plants, located in the membranes of plastids (cytoplasmic organelles bound by a double membrane).

PLASTOCYANIN

Soluble protein found in eukaryotic plants, which contains one atom of copper and is blue when oxidized.

LEADER PEPTIDASE

Enzyme that catalyses the cleavage of the amino-terminal leader sequence from a secreted protein.

GRAM-NEGATIVE BACTERIA

Bacteria whose cell walls do not retain a basic dye during the Gram-stain procedure. These cell walls are thin, consisting of a layer of lipopolysaccharide outside a peptidoglycan layer.

VESICLE TRANSPORT

Transport process during which cargo-containing vesicles bud off from one membrane and are transported to another membrane with which they fuse. This allows lumenal molecules to move from one organelle to the other without ever being in contact with the cytosol.

EUBACTERIA

One of the three main lineages of cellular organism, the other two being Archae and eukaryotes.

BIP

Molecular chaperone in the endoplasmic reticulum that assists protein folding after import.

MITOCHONDRIAL MATRIX

Space enclosed by the mitochondrial inner membrane, which contains enzymes that mediate fatty-acid oxidation and the tricarboxylic-acid cycle.

HSP70

Family of heat-shock proteins, 70 kDa in size. Heat-shock proteins are molecular chaperones that are synthesized by cells that have been exposed to a temperature that is higher than normal.

CHAPERONE

A protein that facilitates the proper folding of other proteins but does not bind to their final folded form.

PROTON MOTIVE FORCE

Proton electrochemical gradient established by energy-transducing membranes.

FLAGELLAR MOTION

Movement of bacteria and some unicellular eukaryotes that is generated using a specialized appendage termed the flagellum.

ATP SYNTHASE

Enzyme that catalyses the phosphorylation of ADP to ATP during oxidative phosphorylation in mitochondria or photophosphorylation in photosynthetic organisms.

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Robinson, C., Bolhuis, A. Protein targeting by the twin-arginine translocation pathway. Nat Rev Mol Cell Biol 2, 350–356 (2001). https://doi.org/10.1038/35073038

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