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Received May 14, 2005; Revision received June 2, 2005
Kinetics of thermal aggregation of model protein substrates (glycogen phosphorylase b from rabbit skeletal muscle and yeast alcohol dehydrogenase) were investigated under heat stress conditions (41-48°C) in the presence of macrophage migration inhibitory factor (MIF), a heat-stable hydrophobic protein (12.5 kD). Anti-chaperone MIF activity found by turbidimetry manifests itself in significantly accelerated protein aggregation and increased limiting value of apparent optical absorption at 360 nm and t → infinity in the sub-stoichiometric range of MIF concentrations. The aggregation kinetics is shown to have cooperative character. Possible reversibility of aggregation after removal of denaturing conditions was demonstrated using alcohol dehydrogenase aggregation at a temperature close to the physiological level (41.5°C). This reversibility is caused by solubility of aggregates and stabilization of oligomeric structure of the substrate as a result of MIF binding to the partially denatured protein. The data suggest that in spite of distinct anti-chaperone effect, the chaperone-like activity of MIF can be observed in the case of heat stress removal and restoration of the system to normal conditions.
KEY WORDS: macrophage migration inhibitory factor, chaperones, anti-chaperones, glycogen phosphorylase b, alcohol dehydrogenase, aggregation, heat stress