The Escherichia coli SRP and SecB targeting pathways converge at the translocon.
Two distinct protein targeting pathways can direct proteins to the Escherichia coli inner membrane. The Sec pathway involves the cytosolic chaperone SecB that binds to the mature region of pre-proteins. SecB targets the pre-protein to SecA that mediates pre-protein translocation through the SecYEG translocon. The SRP pathway is probably used primarily for the targeting and assembly of inner membrane proteins. It involves the signal recognition particle (SRP) that interacts with the hydrophobic targeting signal of nascent proteins. By using a protein cross-linking approach, we demonstrate here that the SRP pathway delivers nascent inner membrane proteins at the membrane. The SRP receptor FtsY, GTP and inner membranes are required for release of the nascent proteins from the SRP. Upon release of the SRP at the membrane, the targeted nascent proteins insert into a translocon that contains at least SecA, SecY and SecG. Hence, as appears to be the case for several other translocation systems, multiple targeting mechanisms deliver a variety of precursor proteins to a common membrane translocation complex of the E.coli inner membrane.
Valent
Q A
QA
Department of Microbiology, Institute of Molecular Biological Sciences, Biocentrum Amsterdam, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands.
Scotti
P A
PA
High
S
S
de Gier
J W
JW
von Heijne
G
G
Lentzen
G
G
Wintermeyer
W
W
Oudega
B
B
Luirink
J
J
D000251:Adenosine Triphosphatases / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D029721:Drosophila Proteins; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008954:Models, Biological; D011499:Protein Processing, Post-Translational; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D018271:Signal Recognition Particle / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D029968:Escherichia coli Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C088616:SecG protein, E coli; C057841:SecY protein, E coli; D018271:Signal Recognition Particle; D014157:Transcription Factors; C036318:signal peptide receptor; C066973:signal sequence receptor; D006160:Guanosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins