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Thermodynamics of substrate binding to the chaperone SecB.
V G Panse1, C P Swaminathan, A Surolia
1Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India.
Biochemistry
|March 1, 2000
Summary
The chaperone SecB binds unfolded polypeptides, with binding thermodynamics revealing key interactions. This study clarifies SecB
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Folding
Background:
- SecB is a chaperone protein crucial for protein folding and secretion.
- Understanding chaperone-substrate interactions is vital for cellular protein homeostasis.
Purpose of the Study:
- To investigate the thermodynamics of unfolded polypeptide binding to the chaperone SecB.
- To elucidate the binding mechanism and stoichiometry of SecB with various substrates.
Main Methods:
- Isothermal titration calorimetry (ITC)
- Fluorescence spectroscopy
- Proteolysis protection assays
Main Results:
- SecB binds both fully unfolded and partially folded polypeptide substrates.
- Heat capacity changes indicate burial of 7-29 residues upon binding.
- Binding stoichiometry is one polypeptide per SecB monomer.
- Evidence supports binding at an exposed hydrophobic cleft, not separate charge/hydrophobic sites.
Conclusions:
- SecB employs a hydrophobic cleft for substrate binding.
- Electrostatic interactions influence SecB aggregation, which is prevented in the absence of substrate.
- The study provides thermodynamic insights into chaperone-substrate recognition.