Chaperone-like effect during in vitro refolding of insulin-like growth factor I using a solubilizing fusion partner

A fusion partner, ZZ, derived from staphylococcal protein A, has earlier been shown facilitate the in vitro folding of human insulin-like growth factor I (IGF-I). Although no solubilizing agents were used, there was no problem with precipitation, even at relatively high protein concentrations. We have here investigated this phenomenon further by characterizing the in vitro refolding of IGF-I fused to one or two solubilizing Z domains. The comparison also included IGF-I without a solubilizing fusion partner. Solubility studies of the reduced proteins were performed, in addition to an evaluation of the aggregation occurring during the refolding process. Fusion to one or two Z domains increased the solubility of reduced IGF-I more than 100-fold. In addition, the Z or ZZ fusion partners decreased aggregation of the IGF-I moieties during the renaturation. The fusion partner has an effect resembling that of a cis-acting chaperone during in vitro refolding and may be an alternative to overcome the problems of insolubility and aggregation.