Remnant signal peptides on non-exported enzymes: implications for the evolution of prokaryotic respiratory chains.
The twin-arginine translocation (Tat) pathway is a prokaryotic protein targeting system dedicated to the transmembrane translocation of folded proteins. Substrate proteins are directed to the Tat translocase by signal peptides bearing a conserved SRRxFLK 'twin-arginine' motif. In Escherichia coli, most of the 27 periplasmically located Tat substrates are cofactor-containing respiratory enzymes, and many of these harbour a molybdenum cofactor at their active site. Molybdenum cofactor-containing proteins are not exclusively located in the periplasm, however, with the major respiratory nitrate reductase (NarG) and the biotin sulfoxide reductase (BisC), for example, being located at the cytoplasmic side of the membrane. Interestingly, both NarG and BisC contain 'N-tail' regions that bear some sequence similarity to twin-arginine signal peptides. In this work, we have examined the relationship between the non-exported N-tails and the Tat system. Using a sensitive genetic screen for Tat transport, variant N-tails were identified that displayed Tat transport activity. For the NarG 36-residue N-tail, six amino acid changes were needed to induce transport activity. However, these changes interfered with binding by the NarJ biosynthetic chaperone and impaired biosynthesis of the native enzyme. For the BisC 36-residue N-tail, only five amino acid substitutions were needed to restore Tat transport activity. These modifications also impaired in vivo BisC activity, but it was not possible to identify a biosynthetic chaperone for this enzyme. These data highlight an intimate genetic and evolutionary link between some non-exported redox enzymes and those transported across membranes by the Tat translocation system.
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Bérengère
B
Ize
Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Sarah J
SJ
Coulthurst
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Kostas
K
Hatzixanthis
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Isabelle
I
Caldelari
Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Grant
G
Buchanan
Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, UK.
Elaine C
EC
Barclay
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
David J
DJ
Richardson
Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Tracy
T
Palmer
Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Frank
F
Sargent
D000595:Amino Acid Sequence; D004579:Electron Transport / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019143:Evolution, Molecular; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D050901:Nitrate Reductase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics*; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid
D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; C408585:twin-arginine translocase complex, E coli; D010088:Oxidoreductases; C019792:biotin sulfoxide reductase; C508365:NarG protein, E coli; D050901:Nitrate Reductase