Mesophase separation and probe dynamics in protein-polyelectrolyte coacervates.

Area of Science:

• Biomaterials Science
• Soft Matter Physics
• Polymer Chemistry

Background:

• Protein-polyelectrolyte coacervates are fluid biomacromolecular assemblies.
• Their unique properties stem from dynamic internal heterogeneities.
• Understanding these structures is key to controlling coacervate behavior.

Purpose of the Study:

• To investigate the structure-dynamics relationship in protein-polyelectrolyte coacervates.
• To probe the influence of pH and ionic strength on coacervate structure.
• To elucidate the mechanisms governing protein diffusion within these complex fluids.

Main Methods:

• Fluorescence recovery after photobleaching (FRAP) to measure self-diffusion.
• Static light scattering (SLS) and cryo-transmission electron microscopy (cryo-TEM) for structural analysis.
• Utilized fluorescein-tagged bovine serum albumin (BSA) and Ficoll for diffusion measurements.

Main Results:

• Coacervates exhibit temporal and spatial heterogeneities with scattering centers of several hundred nm.
• Evidence suggests a structure of dilute domains interspersed with interconnected dense domains (50-700 nm).
• Protein diffusion is length-scale dependent: unobstructed at short scales, slowed by tortuosity and adsorption at intermediate scales, and facilitated by domain break-up at long scales.

Conclusions:

• The observed diffusion patterns are consistent with a heterogeneous domain model.
• Protein mobility is modulated by the complex interplay between dense and dilute phases.
• Findings offer insights into mesophase separation and coacervate behavior, informing future models.