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Related Experiment Videos

Reduced lysozyme in solution and its interaction with non-ionic surfactants.

H Nishiyama1, H Maeda

  • 1Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan.

Biophysical Chemistry
|October 1, 1992
PubMed
Summary

Reduced lysozyme binds poly(oxyethylene) alkylethers through a two-step process, with binding dependent on surfactant concentration relative to its critical micelle concentration (cmc). This study quantifies protein hydrophobicity and characterizes irreversible aggregation mechanisms.

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Area of Science:

  • Biochemistry
  • Protein Chemistry
  • Surface Chemistry

Background:

  • Lysozyme, a common protein, exhibits complex binding interactions with surfactants.
  • Understanding protein-surfactant interactions is crucial for various applications, including drug delivery and protein stabilization.
  • The aggregation behavior of unfolded proteins can lead to irreversible structural changes.

Purpose of the Study:

  • To investigate the binding mechanism of poly(oxyethylene) alkylethers to reduced lysozyme.
  • To quantitatively define the hydrophobicity of reduced lysozyme using binding data.
  • To elucidate the nature of reduced lysozyme aggregation and its pH-dependent characteristics.

Main Methods:

  • Binding isotherms were determined using equilibrium dialysis and surface tension measurements.

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  • Surfactant concentrations were normalized by the critical micelle concentration (cmc) for comparative analysis.
  • A model based on beta-sheet entanglement was used to interpret aggregation phenomena.

    • Main Results:

    • Reduced lysozyme bound surfactants in two steps, with a maximum bound amount (Qmax) of 0.5-0.7 mole surfactant per mole amino acid residue during cooperative binding.
    • Protein hydrophobicity was quantitatively defined as RT ln (cmc/C*), yielding a unique value of 670 J/mol surfactant.
    • Aggregation of reduced lysozyme occurred above pH 2.5, forming aggregates that were only dissociable by lowering the pH, suggesting an irreversible mechanism.

    Conclusions:

    • The binding of poly(oxyethylene) alkylethers to reduced lysozyme is a cooperative process, and Qmax serves as a measure of protein hydrophobicity.
    • The quantitative hydrophobicity value is independent of the specific surfactant used.
    • Irreversible aggregation of reduced lysozyme at higher pH can be explained by an 'entangled' beta-sheet arrangement, applicable to unfolded proteins generally.