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Related Concept Videos

Cooperative Allosteric Transitions01:58

Cooperative Allosteric Transitions

Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand binds to any of these subunits, it triggers a conformational change that affects the binding sites in the other subunits; this can change the affinity of the other sites for their respective ligands. The ability of the protein to change the shape of its binding site is attributed to the presence of a mix of flexible and stable segments in the...
Cooperative Allosteric Transitions01:58

Cooperative Allosteric Transitions

Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand binds to any of these subunits, it triggers a conformational change that affects the binding sites in the other subunits; this can change the affinity of the other sites for their respective ligands. The ability of the protein to change the shape of its binding site is attributed to the presence of a mix of flexible and stable segments in the...
Cooperative Allosteric Transitions01:58

Cooperative Allosteric Transitions

Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand binds to any of these subunits, it triggers a conformational change that affects the binding sites in the other subunits; this can change the affinity of the other sites for their respective ligands. The ability of the protein to change the shape of its binding site is attributed to the presence of a mix of flexible and stable segments in the...
Protein Folding01:25

Protein Folding

Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to its biological function. Interactions between its constituent amino acids guide protein folding, and hence the protein structure is primarily dependent on its amino acid sequence.
Protein Structure Is Critical to Its Biological Function
Proteins perform a wide range of biological functions such as catalyzing chemical reactions, providing...
Protein Folding01:22

Protein Folding

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Protein Folding01:22

Protein Folding

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Related Experiment Video

Updated: May 21, 2026

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability
09:49

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Crowding effect on helix-coil transition: beyond entropic stabilization.

A Koutsioubas1, D Lairez, S Combet

  • 1Laboratoire Léon Brillouin, CEA/CNRS UMR 12, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France.

The Journal of Chemical Physics
|June 16, 2012
PubMed
Summary

Poly(L-glutamic acid) helix formation is stabilized by polyethylene glycol (PEG) crowding agents. However, higher PEG concentrations unexpectedly reduce helix cooperativity, suggesting distinct regimes based on helix length relative to the PEG network mesh size.

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Single-Molecule Measurement of Protein Interaction Dynamics Within Biomolecular Condensates
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Single-Molecule Measurement of Protein Interaction Dynamics Within Biomolecular Condensates

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Area of Science:

  • Biophysics
  • Polymer Science
  • Solution Chemistry

Background:

  • Poly(L-glutamic acid) undergoes helix-coil transitions, a fundamental process in protein folding.
  • Polymer solutions with crowding agents mimic crowded cellular environments.
  • Polyethylene glycol (PEG) is a common crowding agent used in biophysical studies.

Purpose of the Study:

  • To investigate the effect of polyethylene glycol (PEG) as a crowding agent on the helix-coil transition of poly(L-glutamic acid).
  • To understand how PEG concentration influences helix stabilization and cooperativity.
  • To explore the relationship between helix length and the mesh size of the PEG network.

Main Methods:

  • Circular dichroism spectroscopy to monitor helix-coil transitions.
  • Small angle neutron scattering to characterize PEG solution properties and mesh size (ξ).
  • Analysis of helix extent and transition temperature as a function of PEG concentration.

Main Results:

  • Increased PEG concentration stabilizes poly(L-glutamic acid) helices and raises the transition temperature.
  • Higher PEG concentrations unexpectedly decrease helix cooperativity (mean helix extent at transition).
  • A correlation between helix length and PEG mesh size suggests two distinct conformational regimes.

Conclusions:

  • Crowding agents like PEG can stabilize secondary structures but may also impact their cooperative behavior.
  • The observed reduction in cooperativity is not explained by simple entropic stabilization.
  • The findings suggest a dependence of helix properties on the nanoscale architecture of the crowding agent network.