A signal peptide that directs non-Sec transport in bacteria also directs efficient and exclusive transport on the thylakoid Delta pH pathway.
Signal peptides that specifically direct precursor proteins to the thylakoid Delta pH pathway possess an N domain RR motif. Signal peptides that direct transport of bacterial proteins across a non-Sec export pathway possess an N domain RRXFLK consensus motif. Recent genetic studies suggest an evolutionary link between these two protein translocation pathways. To further explore this relationship, we examined the thylakoid targeting capability of the signal peptide for Escherichia coli hydrogenase 1 small subunit (HyaA) by linking it to plastocyanin and assaying the chimeric protein in an in vitro thylakoid transport assay. The chimeric precursor was transported across thylakoids with high efficiency. Transport was characteristic of the Delta pH but not the Sec pathway, i.e. it was eliminated by ionophores that dissipate the DeltapH but occurred in the absence of stromal extract or ATP. This result was confirmed by competition with chemical quantities of a Delta pH pathway precursor. This indicates that the HyaA signal peptide has the necessary elements for efficient and exclusive targeting to the Delta pH pathway and further supports the notion that the alternate targeting pathways in prokaryotes and plant thylakoids are analogous.
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Horticultural Sciences Department and Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, Florida 32611-0690, USA.
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D000251:Adenosine Triphosphatases / Q000737:chemistry; D000595:Amino Acid Sequence; D001120:Arginine; D001426:Bacterial Proteins / Q000737:chemistry; D001692:Biological Transport; D002451:Cell Compartmentation; D002736:Chloroplasts / Q000378:metabolism*; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D006864:Hydrogenase / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D018532:Pisum sativum; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; D001120:Arginine; D006864:Hydrogenase; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins