Proteins represent an important class of therapeutics, however the majority of protein therapies do not readily cross the cell membrane. This largely limits protein therapeutics to extracellular or membrane-bound targets. The development of intracellular protein delivery methods would unlock a range of potential therapeutic avenues from genetic editing to therapeutic antibodies and enzyme replacements. We are developing protein based nanoparticles, called polyelectrolyte complex micelles, to enable intracellular protein delivery. The engineered protein particles self-assemble, driven by electrostatic interactions between a charged polypeptide and an oppositely charged model protein cargo. To create these PEC micelle nanoparticles, we genetically engineered intrinsically disordered protein (IDP) polymers with two distinct domains – a positively charged domain to enable complexation with anionic proteins and an uncharged domain to enable nanoparticle formation. The positively charged domain was based on the disordered region of Histone H5, with variants of altered charge density and length. The uncharged domain was an elastin like polypeptide of varying length. The ability of the biosynthesized block copolypeptides to form stable nanoparticles with model anionic globular protein cargos was evaluated via optical and electron microscopy, as well as dynamic light and small angle x-ray scattering. Engineered IDP features that promote stable particle formation were identified and further engineering to improve cellular uptake and therapeutic release are underway.
