A modified box model including charge regulation for protein adsorption in a spherical polyelectrolyte brush

Area of Science:

• Biophysics
• Polymer Science
• Physical Chemistry

Background:

• Spherical polyelectrolyte brushes (SPB) are known to interact with proteins.
• Bovine serum albumin (BSA) adsorption onto polyacrylic acid SPBs has been experimentally observed, even at pH values above BSA's isoelectric point.

Purpose of the Study:

• To develop a theoretical model describing BSA adsorption in weak polyelectrolyte brushes.
• To explain the experimental observation of significant BSA adsorption under conditions where both the protein and the brush are negatively charged.

Main Methods:

• Construction of a spherical box model for an annealed brush composed of a weak polyelectrolyte.
• Inclusion of BSA adsorption within the theoretical framework.
• Equilibrium conditions were defined by equal BSA chemical potential and zero net force on polyions.

Main Results:

• The model predicts BSA adsorption above its isoelectric point.
• Protein adsorption is highly dependent on ionic strength and pH.
• BSA adsorption is facilitated by a localized pH drop within the brush, causing protein charge reversal.

Conclusions:

• The theoretical model successfully explains BSA adsorption onto SPBs.
• Charge reversal of BSA within the brush environment is the key mechanism for adsorption.
• The findings highlight the importance of local pH and ionic strength in protein-brush interactions.