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© The Rockefeller University Press,
0021-9525/2000//689 $5.00
The Journal of Cell Biology, Volume 150, Number 3,
, 2000 689-694
Report |
Dissecting the Translocase and Integrase Functions of the Escherichia coli Secyeg Translocon
kochhans{at}ruf.uni-freiburg.de
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.
Key Words: membrane proteins • protein transport signal recognition particle • SecA • SecYEG complex
© 2000 The Rockefeller University Press
Abbreviations used in this paper: INV, inside-out inner membrane vesicles; LamB,
receptor; MtlA, mannitol permease; OmpA, outer membrane protein A; SR, SRP receptor, SRP, signal recognition particle.
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