Protein coacervates that separate from the surrounding aqueous phase have a significance in biology to understand the origin of life as well as in diverse engineering fields for many biological applications including protein delivery. Previously, we demonstrated that the recombinant fusion protein complexes, a globular domain fused with a glutamic acid-rich leucine zipper (globule-ZE) and an arginine-rich leucine zipper fused with an elastin-like polypeptide (ZR-ELP), self-assemble into vesicles upon heating through an intermediate coacervate phase. To engineer structural properties of the self-assembled protein vesicles, it is necessary to understand the coacervate-to-vesicle transition and control the coacervate droplets pre-assembled from soluble proteins. Herein, we investigate the kinetics of soluble-coacervate-vesicle phase transition of globule-ZE and ZR-ELP complexes by microscopy and scattering techniques at different temperatures as well as mathematical modeling for two-step protein assembly. The relative concentration of proteins pre-assembled in coacervate droplets to free soluble proteins dictates the kinetics of coacervate growth and vesicle transition. Based on the results, we identify strategies to engineer the size of globular protein vesicles by simply tuning coacervate size via growing time and temperature. This study gives fundamental and practical insights for the development of globular protein-rich colloidal materials including coacervates and vesicles for drug delivery, micro-reactors, and protocell applications.

Study of temperature-induced coacervate-to-vesicle transition of globular fusion proteins towards engineered protein vesicles

2019 Spring National Meeting

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