Facilitated in vitro refolding of human recombinant insulin-like growth factor I using a solubilizing fusion partner

We describe a new approach to refolding recombinant proteins in which an affinity fusion partner, consisting of two IgG-binding domains (ZZ) derived from staphylococcal protein A, is used to solubilize misfolded molecules before, during and after reduction and reoxidation. We show that human insulin-like growth factor I (IGF-I) can be refolded as a fusion protein at a concentration as high as 1-2 mg/ml without the use of denaturing agents. A process scheme suitable for large scale application is described in which the yield of correctly folded human IGF-I with full biological activity is substantially increased.