(634a) Vesicular Protein Suprastructures Via Temperature-Responsive Self-Assembly of Elastin-like Polypeptide Fusion Proteins

Elastin-like polypeptides (ELPs) are artificial peptide repeats derived from tropoelastin. A unique property of ELPs is their inverse transition from the soluble to insoluble phase in aqueous solution during an elevation of temperature. Thus, ELPs can self-assemble into coacervate particles in response to thermal triggers. More interestingly, it is possible to construct self-assembled suprastructures using amphiphilic block copolypeptides of ELP and hydrophilic fragments.^1,2 Here, we describe temperature-responsive self-assembly of vesicular suprastructures using ELP-based fusion proteins that also contain fully folded globular proteins. In our approach, an ELP fragment was fused with a hydrophilic coiled coil protein motif (C1), and served as a hydrophobic fragment of the di-block fusion protein (C1-ELP). For the second building block, we used two fluorescent proteins mCherry and EGFP as model proteins, and constructed di-block fusion proteins, mCherry-C2 and EGFP-C2. Because of high affinity between C1 and its peptide binding partner C2, fusion proteins containing C2 can bind C1-ELP by simply mixing in aqueous solution. When mixture solutions of C1-ELP and mCherry-C2 (or C1-ELP and EGFP-C2) prepared at 4°C were placed at room temperature for an hour, the solutions became turbid, indicating inverse phase transition of ELP motifs and formation of suprastructures. Using confocal microscopy, the resulting protein vesicles were characterized and indicated that the globular fluorescent proteins were homogenously incorporated in the self-assembled layers. Ionic strength of protein solutions played an important role in formation of vesicular suprastructures. We hypothesize that modulation of surface tension by ion concentration allows segregation of ELP fragments in the presence of different types globular proteins, mCherry and EGFP. Our system allows temperature-responsive programmed assembly of engineered recombinant proteins in aqueous environment, without use of any organic solvents, through exploitation of the inverse phase transition behavior of ELP. Incorporation of various types of folded globular proteins including enzymes, growth factors, therapeutic ligands can lead to significant benefits in applications such as biocatalysts, drug delivery, and molecular imaging.

References

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2. M. R. Dreher, A. J. Simnick, K. Fischer, R. J. Smith, A. Patel, M. Schmidt, A. Chilkoti, Temperature triggered self-assembly of polypeptides into multivalent spherical micelles. J. Am. Chem. Soc. 2008, 130, 687 – 694