The binding cascade of SecB to SecA to SecY/E mediates preprotein targeting to the E. coli plasma membrane.
The export of many E. coli proteins such as proOmpA requires the cytosolic chaperone SecB and the membrane-bound preprotein translocase. Translocase is a multisubunit enzyme with the SecA protein as its peripheral membrane domain and the SecY/E protein as its integral domain. SecB, by binding to proOmpA in the cytosol, prevents its aggregation or association with membranes at nonproductive sites. The SecA receptor binds the proOmpA-SecB complex (Kd approximately 6 x 10(-8) M) through direct recognition of both the SecB (Kd approximately 2 x 10(-7) M) as well as the leader and mature domains of the precursor protein. SecB has a dual function in stabilizing the precursor and in passing it on to membrane-bound SecA, the next step in the pathway. SecA itself is bound to the membrane by its affinity (Kd approximately 4 x 10(-8) M) for SecY/E and for acidic lipids. The functions of SecB and SecA as a two-stage receptor system are linked by their affinity for each other.
Hartl
F U
FU
Molecular Biology Institute, University of California, Los Angeles 90024-1570.
Lecker
S
S
Schiebel
E
E
Hendrick
J P
JP
Wickner
W
W
D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008954:Models, Biological; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D000069816:SEC Translocation Channels
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C057841:SecY protein, E coli; C057184:outer membrane protein A precursor (E coli)