Protein vesicles can be synthesized by mixing two fusion proteins; an elastin-like polypeptide (ELP) fused to an arginine rich leucine zipper (Z_R) with a globular, hydrophilic protein fused to a glutamate rich leucine zipper (Z_E). The ELP serves as the hydrophobic block and drives vesicle self-assembly due to a hydrophobic transition that occurs as ELP is heated. Elastin-like polypeptides are repeats of the amino acids VPGXG where X can be any amino acid except proline. Incorporating histidine into the guest residue of the ELP has been demonstrated to allow for the disassembly of ELP containing structures when the pH of the solution is reduced below pH 7.0. Incorporating pH sensitivity into fusion protein vesicles would allow for pH dependent disassembly of vesicles and release of entrapped molecules. In this work, three His-Z_R-ELP fusion proteins with 20, 40, and 60 percent histidine in the ELP guest positions were studied to determine their pH dependent properties. To demonstrate the formation of pH responsive vesicles, the red fluorescent fusion protein mCherry-Z_E was used as the globular, hydrophilic domain. The transition temperature of these mixtures with pH’s between 5.5-8.0 was measured to show that the vesicles are pH responsive and that histidine content in His-Z_R-ELP effects self-assembly. The transition temperature was shown to increase as the pH of the solution decreases and the increase in transition temperature was more drastic for His-Z_R-ELPs with higher histidine content. Additionally, these mixtures were characterized using dynamic light scattering and fluorescent microscopy to show that reducing the pH of the mixture results in the formation of larger, swollen vesicles. These pH sensitive vesicles have the potential to be used in biocatalytic or drug delivery applications where pH dependent release could help ease separations or be utilized for drug release.

Dr. Julie Champion

Associate Professor, Georgia Institute of Technology

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