Effect of ELP Sequence and Fusion Protein Design on Concentrated Solution Self-Assembly

Fusion proteins provide a facile route for the purification and self-assembly of biofunctional protein block copolymers into complex nanostructures; however, the use of biochemical synthesis techniques introduces unexplored variables into the design of the structures. Using model fusion constructs of the red fluorescent protein mCherry and the coil-like protein elastin-like polypeptide (ELP), it is shown that the molar mass and hydrophobicity of the ELP sequence have a large effect on the propensity of a fusion to form well-ordered nanostructures, even when the ELP is in the low temperature, highly solvated state. In contrast, the presence of a 6xHis purification tag has little effect on self-assembly, and the order of blocks in the construct (N-terminal vs C-terminal) only has a significant effect on the nanostructure when the conjugates are heated above the transition temperature of the ELP block. These results indicate that for a sufficiently hydrophobic and high molar mass ELP block, there is a great deal of design latitude in the construction of fusion protein block copolymers for self-assembling nanomaterials.