Protein Purification by Inverse Transition Cycling

Elastin-like polypeptides (ELPs) are environmentally responsive biopolymers based on the elastinderived pentapeptide repeat Val-Pro-Gly-Val-Gly. ELPs undergo a reversible phase transition termed an “inverse temperature transition” (Urry 1992, 1997). Below their transition temperature (Tt), the polypeptides are highly soluble in aqueous solutions. However, when the temperature is raised above Tt, the hydrated polypeptide chains hydrophobically collapse and aggregate, forming a separate, ELP-rich phase. The Tt of an ELP can be conveniently controlled at several different levels. For example, the Tt can be adjusted over a wide range of temperatures through control of the amino acid sequence. The transition can also be triggered isothermally by modulation of environmental conditions, in particular by the type and concentration of added co-solutes. Significantly, ELP fusion proteins, which are produced by joining the gene encoding a protein of interest with an ELP gene segment, can also undergo a reversible phase transition similar to that of the free ELP (Meyer and Chilkoti 1999). Thus, the environmental responsiveness of ELPs