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

F U Hartl1, S Lecker, E Schiebel

  • 1Molecular Biology Institute, University of California, Los Angeles 90024-1570.

Cell
|October 19, 1990
PubMed

Insights

The cytosolic chaperone SecB and membrane-bound SecA protein form a two-stage system essential for E. coli protein export. SecB stabilizes precursor proteins and delivers them to SecA for translocation across the membrane.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Protein Transport

Background:

  • Protein export in E. coli relies on cytosolic chaperones and membrane-bound translocases.
  • The SecB chaperone prevents premature protein aggregation and targets them for export.
  • SecA acts as a receptor and ATPase motor for preprotein translocation.

Purpose of the Study:

  • To elucidate the interaction mechanism between SecB, precursor proteins, and the SecA receptor.
  • To understand the dual role of SecB in precursor stabilization and delivery.
  • To characterize the binding affinities within the protein export machinery.

Main Methods:

  • Biochemical assays to determine binding affinities (Kd values).
  • Analysis of protein-protein interactions in the E. coli protein export pathway.
  • Characterization of the SecA receptor's interaction with SecB-precursor complexes.

Main Results:

  • SecA receptor binds the proOmpA-SecB complex with high affinity (Kd ≈ 6 x 10⁻⁸ M).
  • SecA directly recognizes both SecB and the precursor protein (proOmpA).
  • SecB exhibits a dual function: stabilizing precursors and facilitating transfer to SecA.

Conclusions:

  • SecB and SecA function as a sequential two-stage receptor system for E. coli protein export.
  • The interaction between SecB and SecA is crucial for efficient precursor protein translocation.
  • This system ensures proper targeting and delivery of proteins to the membrane translocase.

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