Dissecting the translocase and integrase functions of the Escherichia coli SecYEG translocon.
Recent evidence suggests that in Escherichia coli, SecA/SecB and signal recognition particle (SRP) are constituents of two different pathways targeting secretory and inner membrane proteins to the SecYEG translocon of the plasma membrane. We now show that a secY mutation, which compromises a functional SecY-SecA interaction, does not impair the SRP-mediated integration of polytopic inner membrane proteins. Furthermore, under conditions in which the translocation of secretory proteins is strictly dependent on SecG for assisting SecA, the absence of SecG still allows polytopic membrane proteins to integrate at the wild-type level. These results indicate that SRP-dependent integration and SecA/SecB-mediated translocation do not only represent two independent protein delivery systems, but also remain mechanistically distinct processes even at the level of the membrane where they engage different domains of SecY and different components of the translocon. In addition, the experimental setup used here enabled us to demonstrate that SRP-dependent integration of a multispanning protein into membrane vesicles leads to a biologically active enzyme.
Institut für Biochemie und Molekularbiologie, Universität Freiburg, 79104 Freiburg, Germany. kochhans@ruf.uni-freiburg.de
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D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D018271:Signal Recognition Particle / Q000378:metabolism*
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli; D018271:Signal Recognition Particle; C078167:OMPA outer membrane proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C022358:mannitol PTS permease, E coli; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins