AGGREGATION OF RECOMBINANT HUMAN INTERFERON-GAMMA - KINETICS AND STRUCTURAL TRANSITIONS

Protein aggregation is a complex phenomenon that can occur in vitro an d in vivo, usually resulting in the loss of the protein's biological a ctivity. While many aggregation studies focus on a mechanism due to a specific stress, this study focuses on the general nature of aggregati on. Recombinant human interferon-gamma (rhIFN-gamma) provides an ideal model for studying protein aggregation, as it has a tendency to aggre gate under mild denaturing stresses (low denaturant concentration, tem perature below the T-m, and below pH 5). All of the aggregates induced by these stresses have a similar structure (high in intermolecular be ta-sheet content and a large loss of alpha-helix) as determined by inf rared and circular dichroism spectroscopy. Thermally induced and denat urant-induced aggregation processes follow first-order kinetics under the conditions of this study. Spectroscopic and kinetic data suggest t hat rhIFN-gamma aggregates through an intermediate form possessing a l arge amount of residual secondary structure. In contrast to the aggreg ates formed under denaturing stresses, the salted-out protein has a re markably nativelike secondary structure.