Supramolecular Protein-Polyelectrolyte Assembly at Near Physiological Conditions-Water Proton NMR, ITC, and DLS Study

Area of Science:

• Biochemistry
• Materials Science
• Immunology

Background:

• The efficacy of polyphosphazene immunoadjuvants depends on their ability to form stable supramolecular complexes with antigens.
• Understanding these protein-polymer interactions is crucial for elucidating immunoadjuvant activity mechanisms.

Purpose of the Study:

• To investigate the self-assembly of a polyphosphazene immunoadjuvant (PCPP) with a model antigen (lysozyme) in a saline solution at neutral pH.
• To characterize the thermodynamics, structural organization, and supramolecular dimensions of these complexes.

Main Methods:

• Isothermal titration calorimetry (ITC) for reaction thermodynamics.
• Water proton nuclear magnetic resonance (wNMR) for water-solute structural organization.
• Dynamic light scattering (DLS) for supramolecular dimensions.

Main Results:

• Complex formation between lysozyme and PCPP was confirmed under near-physiological conditions by all employed methods.
• Thermodynamic analysis indicated a dissociation constant in the micromolar range, with enthalpy dominating the interactions.
• Avidity of the complexes was influenced by the physical state and dimensions of the assemblies.

Conclusions:

• The findings support a model of protein charge anisotropy and polymer properties favoring high-affinity complex formation.
• The study highlights the utility of wNMR for analyzing protein-polymer interactions, particularly in low protein-load scenarios.