Directly visualizing individual polyorganophosphazenes and their single-chain complexes with proteins

Area of Science:

• Macromolecular science
• Biophysical chemistry
• Materials science

Background:

• Polyorganophosphazenes are water-soluble macromolecules with immunoadjuvant properties.
• They self-assemble with proteins, enabling biological functions crucial for drug delivery systems.

Purpose of the Study:

• To visualize the structure of polyorganophosphazenes and their protein assemblies using direct imaging techniques.
• To understand the supramolecular assembly processes and mechanistic aspects of polymer-enabled vaccine delivery.

Main Methods:

• Direct imaging by cryogenic electron microscopy (cryo-EM) to visualize individual polymer chains.
• Atomic force microscopy (AFM) to support morphology outcomes.
• Advanced analytical techniques to confirm protein-polymer binding.

Main Results:

• Cryo-EM successfully visualized the coil structure of highly charged polyorganophosphazenes in a vitrified state without additives.
• Multiple protein copies were observed binding at the single polymer chain level, forming compact spherical complexes or stiffened coils.
• Morphological insights crucial for understanding biological activity were obtained, which are not deducible by techniques like light scattering.

Conclusions:

• Direct imaging provides crucial morphological insights into polyorganophosphazene-protein assemblies.
• The visualization methodology offers tools for understanding supramolecular assembly and polymer-enabled vaccine delivery mechanisms.