Zinc-Mediated Loading and Release of His-Tagged Recombinant Proteins in Self-Assembling Peptide Coacervates

The development of tunable systems for subcutaneous injection is currently the focus of exploratory protein formulation. For the delivery of protein biologics intended for extended release, a high fraction of the drug that escapes from the deposition site ("burst release") may pose safety concerns. Herein, we report an injectable system of bioaffinity zinc-containing peptide coacervates in which recombinant proteins coexpressed with histidine (His)-tags can be captured and released over time. Coacervates are formed by driving self-assembling peptide (SAP), AEAEAKAKAEAEAKAKHHHHHH (EAKH6) β-sheet dimers, into cross-linking fibrils. In the presence of Zn²⁺, the fibrillization of EAKH6 is enhanced through the interaction of metal ions with histidine residues in the peptide. The Zn²⁺:EAKH6 scaffold retains His-tagged proteins both in vitro and in vivo and extends their duration of release. The results present a case study in which the Zn²⁺-[His]₆ interaction can be used to tune the properties of supramolecular structures and the loading of His-tagged proteins.