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SecA folds via a dimeric intermediate.

S M Doyle1, E H Braswell, C M Teschke

  • 1Department of Molecular and Cell Biology and National Center for Analytical Ultracentrifugation, University of Connecticut, Storrs, Connecticut 06269-3125, USA.

Biochemistry
|September 20, 2000
PubMed
Summary
This summary is machine-generated.

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SecA protein folding was studied using urea and fluorescence. Researchers found SecA unfolds via a dimeric intermediate before dissociating, revealing its stability and folding pathway.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Protein Folding Dynamics

Background:

  • Many cellular proteins are large and multimeric, yet their folding mechanisms remain understudied.
  • SecA, a homodimeric protein crucial for bacterial protein translocation, is a relevant model due to its size and potential partial unfolding during membrane insertion.

Purpose of the Study:

  • To investigate the folding pathway and stability of the bacterial protein SecA.
  • To understand how SecA's structure relates to its function in preprotein translocation.

Main Methods:

  • Kinetic and equilibrium folding monitored using circular dichroism and tryptophan fluorescence.
  • Equilibrium folding also assessed with a fluorescent ATP analogue.
  • Protein stability confirmed via analytical ultracentrifugation (equilibrium and velocity sedimentation).

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Main Results:

  • A three-state folding model was proposed: N(2) -> I(2) -> 2U, involving a dimeric intermediate.
  • SecA dimer exhibits significant stability (ΔG = -22.5 kcal/mol).
  • The rate-limiting step is the conversion of the dimeric intermediate to the native dimer; unfolding is slow.

Conclusions:

  • SecA functions as a stable dimer, making monomer dissociation during translocation improbable.
  • Understanding SecA's folding pathway provides insights into its essential role in the Sec-dependent translocase system.