Structural diversity in twin-arginine signal peptide-binding proteins.
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 Tat-dependent 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.
Maillard
Julien
J
Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
Spronk
Chris A E M
CA
Buchanan
Grant
G
Lyall
Verity
V
Richardson
David J
DJ
Palmer
Tracy
T
Vuister
Geerten W
GW
Sargent
Frank
F
D001120:Arginine / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D014644:Genetic Variation; D026901:Membrane Transport Proteins / Q000378:metabolism*; D050901:Nitrate Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D021382:Protein Sorting Signals / Q000502:physiology*; D015398:Signal Transduction; D013379:Substrate Specificity
D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C524414:NapD protein, E coli; D021382:Protein Sorting Signals; C408585:twin-arginine translocase complex, E coli; D001120:Arginine; D050901:Nitrate Reductase; C494404:napA protein, E coli