The Escherichia coli expression system is a preferable choice for production of recombinant proteins. A disadvantage of this system is the target protein aggregation in "inclusion bodies" (IBs) that further requires solubilisation and refolding, which is crucial for the properties and the yield of the final product. In order to prevent aggregation, SUMO fusion tag technology has been successfully applied for expression of eukaryotic proteins, including human interferon gamma (hIEN gamma) that was reported, however, with no satisfactory biological activity. We modified this methodology for expression and purification of both the wild type hIEN gamma and an extremely prone to aggregation mutant hIEN gamma-K88Q whose recovery from IBs showed to be ineffective upon numerous conditions. By expression of the N-terminal His-SUMO fusion proteins in the E. coli strain BL21(DE3)pG-KJE8, co-expressing two chaperone systems, at 24 degrees C a significant increase in solubility of both target proteins (1.5-fold for hIEN gamma and 8-fold for K88Q) was achieved. Two-step chromatography (affinity and ion-exchange) with on-dialysis His-SUMO-tag cleavage was applied for protein purification that yielded 6.0-7.0 mg/g wet biomass for both proteins with >95% purity and native N-termini. The optimised protocol led to increased yields from 5.5 times for hIEN gamma up to 100 times for K88Q in comparison to their isolation from IBs. Purified hIFN gamma showed preserved thermal stability and antiproliferative activity corresponding to that of the native reference sample (3 x 10(7) IU/mg). The developed methodology represents an optimised procedure that can be successfully applied for large scale expression and purification of aggregation-prone proteins in soluble native form. (C) 2015 Elsevier Inc. All rights reserved.