Isoelectric point (pI)‐based phase separation (pI‐BPS) purification of elastin‐like polypeptides (ELPs) containing charged, biologically active fusion proteins (ELP‐FPs)

Abstract

AbstractElastin‐like polypeptides (ELPs) are peptide‐based biomaterials with residue sequence (VPGXG)n where X is any residue except proline. ELPs are a useful modality for delivering biologically active proteins (growth factors, protease inhibitors, anti‐inflammatory peptides, etc.) as fusion proteins (ELP‐FP). ELP‐FPs are particularly cost‐effective because they can be rapidly purified using Inverse Temperature Cycling (ITC) via the reversible formation and precipitation of entropically driven aggregates above a transition temperature (Tt). When ELP fusion proteins (ELP‐FPs) contain significant charge density at physiological pH, electrostatic repulsion between them severely inhibits aggregate formation. The literature does not currently describe methods for purifying ELP‐FPs containing charged proteins on either side of the ELP sequence as fusion partners without organic solvents. Here, the isoelectric point (pI) of ELP‐FPs is discussed as a means of neutralizing surface charges on ELP‐FPs and increasing ITC yield to dramatically high levels. We use pI‐based phase separation (pI‐BPS) to purify ELP‐FPs containing cationic and anionic fusion proteins. We report a dramatic increase in protein yield when using pI‐BPS for purification of ELP‐FPs. Proteins purified by this method also retain the functional activity of the protein present in the ELP‐FP. Techniques developed here enable significant diversification of possible fusion proteins delivered by ELPs as ELP‐FPs by allowing them to be produced and purified at higher quantities and yields.