Topological Effects on Globular Protein-ELP Fusion Block Copolymer Self-Assembly

Perfectly defined, monodisperse fusion protein block copolymers of a thermoresponsive coil-like protein, ELP, and a globular protein, mCherry, are demonstrated to act as fully biosynthetic analogues to protein-polymer conjugates that can self-assemble into biofunctional nanostructures such as hexagonal and lamellar phases in concentrated solutions. The phase behavior of two mCherry-ELP fusions, E-10-mCherry-E-10 and E-20-mCherry, is investigated to compare linear and bola fusion self-assembly both in diluted and concentrated aqueous solution. In dilute solution, the molecular topology impacts the stability of micelles formed above the thermal transition temperature of the ELP block, with the diblock forming micelles and the bola forming unstable aggregates. Despite the chemical similarity of the two protein blocks, the materials order into block copolymer-like nanostructures across a wide range of concentrations at 30 wt% and above, with the bola fusion having a lower order-disorder transition concentration than the diblock fusion. The topology of the molecule has a large impact on the type of nanostructure formed, with the two fusions forming phases in the opposite order as a function of temperature and concentration. This new system provides a rich landscape to explore the capabilities of fusion architecture to control supramolecular assemblies for bioactive materials.