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Related Concept Videos

Molecular Chaperones and Protein Folding03:00

Molecular Chaperones and Protein Folding

The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
The...

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Detection of the pH-dependent Activity of Escherichia coli Chaperone HdeB In Vitro and In Vivo
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Direct demonstration that homotetrameric chaperone SecB undergoes a dynamic dimer-tetramer equilibrium.

T B Topping1, R L Woodbury, D L Diamond

  • 1School of Molecular Biosciences, Washington State University, Pullman 99164-4660, USA. topping@wsu.edu

The Journal of Biological Chemistry
|December 9, 2000
PubMed
Summary

The bacterial chaperone SecB exists as a dimer of dimers, dynamically interconverting between dimer and tetramer states. Cysteine residues are crucial for stabilizing the tetramer

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Protein Structure

Background:

  • SecB is a cytosolic bacterial chaperone essential for protein translocation.
  • Chaperones play critical roles in maintaining cellular proteostasis.
  • Understanding SecB's quaternary structure is key to its function.

Purpose of the Study:

  • To elucidate the native quaternary structure and assembly dynamics of the bacterial chaperone SecB.
  • To investigate the role of cysteine residues in SecB oligomerization.

Main Methods:

  • Size exclusion chromatography to analyze protein size and interactions.
  • Native polyacrylamide gel electrophoresis (native PAGE) to assess protein assembly.
  • Chemical modification using 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) to probe disulfide bond involvement.

Main Results:

  • SecB exists in a dynamic equilibrium between dimer and tetramer forms in solution.
  • Mixing distinct tetrameric SecB species resulted in the formation of a hybrid tetramer, confirming dimer exchange.
  • Chemical modification of cysteine residues with DTNB led to irreversible dissociation to dimers, indicating their role in stabilizing the tetramer.

Conclusions:

  • SecB forms a structural dimer of dimers, with differential stability at the dimer-dimer interfaces.
  • One dimer interface is less stable, allowing for dynamic dimer-tetramer equilibrium.
  • Cysteine residues are critical for the stability of the tetrameric structure of SecB.