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Proc Natl Acad Sci U S A. 2007 Oct 2;104(40):15641-6. Epub 2007 Sep 27.

Structural diversity in twin-arginine signal peptide-binding proteins.

Author information

1
Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.

Abstract

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.

PMID:
17901208
PMCID:
PMC2000414
DOI:
10.1073/pnas.0703967104
[Indexed for MEDLINE]
Free PMC Article

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