Interferon-gamma is a target for binding and folding by both Escherichia coli chaperone model systems GroEL/GroES and DnaK/DnaJ/GrpE

IFN-gamma can be physicochemically distinguished from interferons-alpha, -b eta or -omega through the loss of its tertiary structure and biological act ivity upon exposure to acid or heat. This loss is due to the irreversible a ggregation of an unfolded or partially folded state. The conformational ins tability of IFN-gamma is reflected by its impairment to fold properly when overexpressed in Escherichia coli, resulting in its accumulation in cytopla smic inclusion bodies. Chaperones were originally identified as a heterogen eous group of proteins that mediate the folding and correct assembly of var ious polypeptide substrates, and protect thermolabile proteins against inac tivation. In either of both cases, chaperones prevent irreversible misfoldi ng by assisting the substrate protein along its pathway to a stable tertiar y conformation. Among the best characterized chaperones are the Escherichia coli Hsp60 and Hsp70 heat shock protein complexes, i.e., GroEL/GroES and D naK/DnaJ/GrpE. They exhibit entirely different reaction mechanisms, which, however, both depend on hydrolysis of ATP. The unfolding of recombinant IFN -gamma by acid or heat can be used as a tool to assess its in vitro interac tion with each of both chaperone systems at physiological temperature (35 d egrees C). Using such an experimental set-up, both the DnaK and GroEL chape rone systems appeared to form complexes with IFN-gamma from which correctly folded protein was released in an ATP-dependent manner. In addition to the biotechnological implication of these observations, the relevance to de no vo folding of IFN-gamma is discussed. (C) Societe francaise de biochimie et biologie moleculaire/Elsevier, Paris.