Unexpected Multivalent Display of Proteins by Temperature Triggered Self-Assembly of Elastin-like Polypeptide Block Copolymers

We report herein the unexpected temperature triggered self-assembly of proteins fused to thermally responsive elastin-like polypeptides (ELPs) into spherical micelles. Six ELP block copolymers (ELPBC) with different hydrophilic and hydrophobic block lengths were genetically fused to two single domain proteins, thioredoxin (Trx) and a fibronectin type III domain (Fn3) that binds the αvβ3 integrin. The self-assembly of these protein-ELPBC fusions as a function of temperature was investigated by UV spectroscopy, light scattering, and cryo-TEM. Self-assembly of the ELPBC was –unexpectedly- retained upon fusion to the two proteins, resulting in the formation of spherical micelles with a hydrodynamic radius that ranged from 24–37 nm, depending on the protein and ELPBC. Cryo-TEM images confirmed the formation of spherical particles with a size that was consistent with that measured by light scattering. The bioactivity of Fn3 was retained when presented by the ELPBC micelles as indicated by the enhanced uptake of the Fn3-decorated ELPBC micelles in comparison to the unimer by cells that overexpress the αvβ3 integrin. The fusion of single domain proteins to ELPBCs may provide a ubiquitous platform for the multivalent presentation of proteins