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Determination of Plasma Membrane Partitioning for Peripherally-associated Proteins
Published on: June 15, 2018
Membrane partitioning: "classical" and "nonclassical" hydrophobic effects
Mónica Fernández-Vidal1, Stephen H White, Alexey S Ladokhin
1Department of Physiology and Biophysics, University of California, Irvine, CA 92697-4560, USA.
The Journal of Membrane Biology
|December 9, 2010
Summary
Membrane partitioning is driven by the classical hydrophobic effect, not a "nonclassical" one. Melittin
Area of Science:
- Biophysics
- Membrane Biology
- Thermodynamics
Background:
- Nonpolar solute transfer to lipid bilayers often shows negative enthalpy, contradicting the expected positive entropy of the hydrophobic effect.
- This has led to the hypothesis of a
- nonclassical
- hydrophobic effect driving membrane partitioning.
Purpose of the Study:
- To investigate the driving forces behind peptide partitioning into lipid bilayers.
- To determine if a "nonclassical" hydrophobic effect is necessary to explain membrane partitioning phenomena.
Main Methods:
- Characterization of melittin partitioning using isothermal titration calorimetry (ITC) and circular dichroism (CD).
- Studying the temperature dependence of entropic and enthalpic free energy components of partitioning.
- Analysis of partitioning into lipid membranes with varying zwitterionic and anionic lipid compositions and vesicle sizes.
Main Results:
- Significant variations in entropic and enthalpic components with temperature, lipid composition, and vesicle size were observed, alongside entropy-enthalpy compensation.
- A large negative heat capacity (-0.5 kcal mol(-1) K(-1)), independent of lipid composition, was measured, characteristic of the hydrophobic effect.
- Hydrophobic-effect free energy (ΔG(hΦ)) dominated melittin partitioning, irrespective of lipid composition.
Conclusions:
- The classical hydrophobic effect adequately explains peptide partitioning into lipid bilayers.
- A "nonclassical" hydrophobic effect is not required to describe these partitioning phenomena.
- Coulombic attraction contributes to partitioning in anionic membranes, but hydrophobic interactions remain dominant.
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