The association of unfolding intermediates during the equilibrium unfolding of recombinant murine interleukin-6

Publisher Summary This chapter discusses the association of unfolding intermediates during the equilibrium unfolding of recombinant murine interleukin-6. Interleukin-6 (IL-6) is a multifunctional cytokine that acts by binding to a specific cell membrane receptor protein (IL-6R) and a signal transducing protein, gpl30. The presence of equilibrium unfolding intermediates can be detected by the non-coincidence of unfolding transitions as monitored by fluorescence and far-UV circular dichroism (CD) spectroscopy. The major difference between the two denaturants is that, GdnHCl is ionic whereas urea is not. To determine if intermediate formation was concentration dependent, the fluorescence emission spectrum of mIL-6 as a function of protein concentration was monitored in the study described in the chapter. Fluorescent properties of the aggregates observed in nuclear magnetic resonance (NMR) experiments are identical to the intermediates in the equilibrium experiments, suggesting that the intermediate formation in both cases is the same.