Spectrophotometric Insights into Protein Encapsulation in Polyelectrolyte Complex Micelles

In this presentation, we discuss the evolution of protein structure and aggregation states upon their encapsulation into polyelectrolyte complex (PEC) micelles as well provide insights into the local environment in the PEC domains. PEC micelles are nanosized complexes self-assembled in aqueous milieu via electrostatic interactions between oppositely charged diblock polyelectrolytes. The charged, hydrophilic, and polymer-dense environment of PEC domains have been shown to sequester and protect enzymes and nucleic acids, and these micelles have been suggested as potential therapeutic and biomedical carriers. Yet, the local environments in their PEC domains remain poorly understood. To address these knowledge gaps, we created a library of diblock polyelectrolyte pairs with varying charged-block lengths, formed PEC micelles (with and without encapsulated protein), and employed light scattering techniques to determine their hydrodynamic radii, core radii, and shape, and compare them against theoretical scaling relationships. To gain insight into the PEC domain environment, we encapsulated fluorescein-tagged bovine serum albumin (F-BSA) in PEC micelles and utilized fluorescence spectroscopy to correlate spectral shifts with the oligomerization state of F-BSA. Our data characterize the structure and dynamics of PEC micelles and demonstrate the feasibility of characterizing the nanoscale local environment of PEC domains using fluorescence spectroscopy.