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

170

The twin-arginine translocation (Tat) machinery transports folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of chloroplasts. It has been inferred that the Tat translocation site is assembled on demand by substrate-induced association of the protein TatA. We tested this model by imaging YFP-tagged TatA expressed at native levels in living Escherichia coli cells in the presence of low levels of the TatA paralogue TatE. Under these conditions the TatA-YFP fusion supports full physiological Tat transport activity. In agreement with the TatA association model, raising the number of transport-competent substrate proteins within the cell leads to an increase in the number of large TatA complexes present. Formation of these complexes requires both a functional TatBC substrate receptor and the transmembrane proton motive force (PMF). Removing the PMF causes TatA complexes to dissociate, except in strains with impaired Tat transport activity. Based on these observations we propose that TatA assembly reaches a critical point at which oligomerization can be reversed only by substrate transport. In contrast to TatA-YFP, the oligomeric states of TatB-YFP and TatC-YFP fusions are not affected by substrate or the PMF, although TatB-YFP oligomerization does require TatC.

mentioning

confidence: 99%

Live cell imaging shows reversible assembly of the TatA component of the twin-arginine protein transport system

Alcock

Baker

Greene

et al. 2013

170

“…Precursors bearing Tat signal peptides are transported by a membrane embedded export apparatus comprising a signal peptide recognition complex (4) and a protein-conducting channel (5). The physiological role of the Tat system is to transport fully folded proteins (1,6,7), and pathogenic bacteria deficient in Tat transport demonstrate reduced virulence, which has led to consideration of this system as a target for novel antiinfectives (8). The model eubacterium Escherichia coli produces 27 Tattargeted proteins (9).…”

mentioning

confidence: 99%

Structural diversity in twin-arginine signal peptide-binding proteins

Maillard

Spronk

Buchanan

et al. 2007

The twin-arginine transport (Tat) system is dedicated to the translocation of folded proteins across the bacterial cytoplasmic membrane. Proteins are targeted to the Tat system by signal peptides containing a twin-arginine motif. In Escherichia coli, many Tat substrates bind redox-active cofactors in the cytoplasm before transport. Coordination of cofactor insertion with protein export involves a ''Tat proofreading'' process in which chaperones bind twin-arginine signal peptides, thus preventing premature export. The initial Tat signal-binding proteins described belonged to the TorD family, which are required for assembly of N-and S-oxide reductases. Here, we report that E. coli NapD is a Tat signal peptide-binding chaperone involved in biosynthesis of the Tatdependent nitrate reductase NapA. NapD binds tightly and specifically to the NapA twin-arginine signal peptide and suppresses signal peptide translocation activity such that transport via the Tat pathway is retarded. High-resolution, heteronuclear, multidimensional NMR spectroscopy reveals the 3D solution structure of NapD. The chaperone adopts a ferredoxin-type fold, which is completely distinct from the TorD family. Thus, NapD represents a new family of twin-arginine signal-peptide-binding proteins.metalloenzyme biosynthesis ͉ molecular chaperone ͉ NMR solution structure ͉ protein-protein interactions ͉ twin-arginine transport pathway

“…This system does not depend on the hydrolysis of ATP; instead, it is driven by proton concentration differences (⌬pH) across the thylakoid membrane (6). Subsequently, in 1997 Settles et al (7) reported the identification of a specific chloroplast membrane protein (Hcf106) required for the Sec-independent secretion of proteins into plant thylakoids, and interestingly, they found that Hcf106 is closely related to a bacterial protein.…”

mentioning

confidence: 99%

Effects of the twin-arginine translocase on secretion of virulence factors, stress response, and pathogenesis

Ochsner

Snyder

Vasil

et al. 2002

189

226

A novel secretion pathway originally found in plants has recently been discovered in bacteria and termed TAT, for ''twin-arginine translocation,'' with respect to the presence of an Arg-Arg motif in the signal sequence of TAT-secreted products. However, it is unknown whether the TAT system contributes in any way to virulence through the secretion of factors associated with pathogenesis or stress response. We found that the opportunistic pathogen Pseudomonas aeruginosa produces several virulence factors that depend on the TAT system for proper export to the periplasm, outer membrane, or extracellular milieu. We identified at least 18 TAT substrates of P. aeruginosa and characterized the pleiotropic phenotypes of a tatC deletion mutant. The TAT system proved essential for the export of phospholipases, proteins involved in pyoverdine-mediated ironuptake, anaerobic respiration, osmotic stress defense, motility, and biofilm formation. Because all these traits have been associated with virulence, we studied the role of TAT in a rat lung model. A tatC mutant did not cause the typical multifocal pulmonary abscesses and did not evoke a heavy inflammatory host response compared with wild type, indicating that tatC mutant cells are attenuated for virulence. Because the TAT apparatus is well conserved among important bacterial pathogens yet absent in mammalian cells, it represents a potential target for novel antimicrobial compounds.