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

• Main Authors: Antsje Nolles, Adrie H. Westphal, J. Mieke Kleijn, Willem J. H. van Berkel, Jan Willem Borst
• Format: Article
• Language: English
• Published: MDPI AG 2017-07-01
• Series: International Journal of Molecular Sciences
• Subjects: Anthozoa; chromophore; circular dichroism; diblock copolymer; dynamic light scattering; fluorescence correlation spectroscopy; Hydrozoa; polyelectrolyte; protein structure; steady-state fluorescence
• Online Access: https://www.mdpi.com/1422-0067/18/7/1557

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 (anFPs) than for Hydrozoa FPs derived from Aequorea victoria (avFPs). Far-UV CD spectra of the free FPs showed remarkable differences between avFPs and anFPs, caused by rounder barrel structures for avFPs and more elliptic ones for anFPs. These structural differences, along with the differences in charge distribution, might explain the variations in encapsulation efficiency between avFPs and anFPs. Furthermore, the avFPs remain monomeric in C3Ms with minor spectral and structural changes. In contrast, the encapsulation of anFPs gives rise to decreased quantum yields (monomeric Kusabira Orange 2 (mKO2) and Tag red fluorescent protein (TagRFP)) or to a pKa shift of the chromophore (FP variant mCherry).