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The binding cascade of SecB to SecA to SecYE mediates preprotein targeting to the E. coli plasma membrane

1990; Cell Press; Volume: 63; Issue: 2 Linguagem: Inglês

10.1016/0092-8674(90)90160-g

1097-4172

F. Ulrich Hartl, Stewart H. Lecker, Elmar Schiebel, Joseph P. Hendrick, William Wickner,

RNA and protein synthesis mechanisms

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 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 ≈ 6 × 10−8 M) through direct recognition of both the SecB (Kd ≈ 2 × 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 ≈ 4 × 10−8 M) for and for acidic lipids. The functions of SecB and SecA as a two-stage receptor system are linked by their affinity for each other.