Colorful Packages: Encapsulation of Fluorescent Proteins in Complex Coacervate Core Micelles.

Encapsulation of proteins can be beneficial for food and biomedical applications. To study their biophysical properties in complex coacervate core micelles (C3Ms), we previously encapsulated enhanced green fluorescent protein (EGFP) and its monomeric variant, mEGFP, with the cationic-neutral diblock copolymer poly(2-methyl-vinyl-pyridinium)n - b -poly(ethylene-oxide)m (P2MVPn - b -PEOm ) as enveloping material. C3Ms with high packaging densities of fluorescent proteins (FPs) were obtained, resulting in a restricted orientational freedom of the protein molecules, influencing their structural and spectral properties. To address the generality of this behavior, we encapsulated seven FPs with P2MVP41 - b -PEO205 and P2MVP128 - b -PEO477 . Dynamic light scattering and fluorescence correlation spectroscopy showed lower encapsulation efficiencies for members of the Anthozoa class ( an FPs) than for Hydrozoa FPs derived from Aequorea victoria ( av FPs). Far-UV CD spectra of the free FPs showed remarkable differences between av FPs and an FPs, caused by rounder barrel structures for av FPs and more elliptic ones for an FPs. These structural differences, along with the differences in charge distribution, might explain the variations in encapsulation efficiency between av FPs and an FPs. Furthermore, the av FPs remain monomeric in C3Ms with minor spectral and structural changes. In contrast, the encapsulation of an FPs gives rise to decreased quantum yields (monomeric Kusabira Orange 2 (mKO2) and Tag red fluorescent protein (TagRFP)) or to a p K a shift of the chromophore (FP variant mCherry).