The signal recognition particle-targeting pathway does not necessarily deliver proteins to the sec-translocase in Escherichia coli.
ProW is an Escherichia coli inner membrane protein that consists of a 100-residue-long periplasmic N-terminal tail (N-tail) followed by seven closely spaced transmembrane segments. N-tail translocation presumably proceeds in a C-to-N-terminal direction and represents a poorly understood aspect of membrane protein biogenesis. Here, using an in vivo depletion approach, we show that N-tail translocation in a ProW derivative comprising the N-tail and the first transmembrane segment fused to the globular P2 domain of leader peptidase depends both on the bacterial signal recognition particle (SRP) and the Sec-translocase. Surprisingly, however, a deletion construct with only one transmembrane segment downstream of the N-tail can assemble properly even under severe depletion of SecE, a central component of the Sec-translocase, but not under SRP-depletion conditions. To our knowledge, this is the first demonstration that the SRP-targeting pathway does not necessarily deliver SRP-dependent inner membrane proteins to the Sec-translocase. The data further suggest that N-tail translocation can proceed in the absence of a functional Sec-translocase.
Cristóbal
S
S
Department of Biochemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
Scotti
P
P
Luirink
J
J
von Heijne
G
G
de Gier
J W
JW
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins; D001692:Biological Transport; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C490210:ProW protein, E coli; D018271:Signal Recognition Particle