The twin-arginine translocation (Tat) protein export pathway

• Published in: Nature reviews. Microbiology 2012-07, Vol.10 (7), p.483-496
• Main Authors: Palmer, Tracy, Berks, Ben C.
• Format: Article
• Language: English
• Subjects: 26; 41; 631/326/26/2527; 631/326/41/1969; 631/80/2023/2022; 88; Bacteria; Biomedical and Life Sciences; Cell Membrane - physiology; Cell membranes; Chloroplasts; E coli; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Gene Expression Regulation, Bacterial - physiology; Genomes; Infectious Diseases; Ions; Life Sciences; Medical Microbiology; Membrane proteins; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Membranes; Microbiology; Mitochondria; Organisms; Parasitology; Peptides; Physiological aspects; Proteins; review-article; Translocation; Virology
• ISSN: 1740-1526; 1740-1534
• DOI: 10.1038/nrmicro2814

Key Points The twin-arginine translocation (Tat) pathway transports folded proteins across the cytoplasmic membrane of most bacteria and archaea. Proteins are targeted to the Tat machinery by signal peptides containing a conserved twin-arginine motif. Some proteins need to be folded before transport because they contain redox cofactors that are inserted in the cytoplasm, or to avoid insertion of the incorrect metal ion cofactor at the active site. In some cases, dedicated chaperones ensure cofactor insertion before protein targeting to the Tat pathway. Bacteria and archaea can have differential requirements for the Tat transport system. It is essential in some organisms, non-essential in others and completely absent in certain bacteria and archaea. Furthermore, the number of Tat substrates varies widely among different organisms. The Escherichia coli Tat machinery comprises three proteins: TatA, TatB and TatC. The TatBC complex binds Tat substrate proteins through their signal peptides. TatA is recruited to the activated TatBC complex and mediates transport of the substrate. TatA exists as monomers or small oligomers and polymerizes during Tat-mediated substrate transport. The transmembrane and amphipathic helices of TatA are essential regions of the protein, each undergoing self-interaction during TatA oligomerization. TatA may form an aqueous channel through which substrate is transported or may deform the membrane to allow re-orientation of the polar phospholipid head groups around the substrate during transport. The twin-arginine translocation (Tat) protein export system is present in the membranes of most bacteria and archaea and transports folded proteins while maintaining the permeability barrier of the membrane. Here, Palmer and Berks summarize the recent advances in our understanding of how this remarkable system functions. The twin-arginine translocation (Tat) protein export system is present in the cytoplasmic membranes of most bacteria and archaea and has the highly unusual property of transporting fully folded proteins. The system must therefore provide a transmembrane pathway that is large enough to allow the passage of structured macromolecular substrates of different sizes but that maintains the impermeability of the membrane to ions. In the Gram-negative bacterium Escherichia coli , this complex task can be achieved by using only three small membrane proteins: TatA, TatB and TatC. In this Review, we summarize recent advances in our underst