Proton-coupled protein binding: controlling lysozyme/poly(acrylic acid) interactions with pH
Ananta Ghimire1, Rajeswari M Kasi, Challa V Kumar
1Department of Chemistry, U-3060, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
The Journal of Physical Chemistry. B
|April 18, 2014
Summary
Understanding protein-polymer interfaces is key for designing responsive materials. This study shows pH-dependent binding of lysozyme to poly(acrylic acid), controlled by charge neutralization, enabling tunable protein interactions.
Area of Science:
- Biomaterials Science
- Polymer Chemistry
- Physical Chemistry
Background:
- Rational design of protein-polymer composites requires understanding macromolecular interactions.
- Protein-polymer interfaces are crucial for stimuli-responsive materials in various applications.
Purpose of the Study:
- To investigate the binding interactions between poly(acrylic acid) (PAA) and lysozyme.
- To elucidate the role of pH and charge neutralization in governing these interactions.
- To explore the potential for stimuli-responsive protein binding and release.
Main Methods:
- Isothermal titration calorimetry (ITC) was employed to study lysozyme-PAA binding.
- Binding thermodynamics (ΔH, TΔS, ΔG) and stoichiometry were measured across a pH range (3-8).
- The influence of pH on complex size and binding mechanism was analyzed.
Main Results:
- Strong exothermic binding of lysozyme to PAA was observed, with thermodynamics dependent on pH.
- Binding stoichiometry significantly increased with pH, from 1:1 to 16:1 (lysozyme:PAA).
- Binding affinity (ΔG) remained largely pH-independent, while enthalpy and entropy varied predictably.
Conclusions:
- Protonation-deprotonation of the protein-polymer interface plays a major role in binding.
- "Charge neutralization" governs binding stoichiometry and thermodynamics but not affinity.
- The pH-dependent binding mechanism offers a stimuli-responsive system for protein complexation and release.
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