The solution structure and conformational dynamics of tumor necrosis factor-alpha and a (Cys69----Asp; Cys101----Arg) analog as examined by IR spectroscopy and hydrogen exchange.

An analog of human tumor necrosis factor-alpha (TNF-alpha) was created with Cys69 and Cys101 replaced with Asp and Arg respectively. We have undertaken a comparative study of the solution conformation and dynamics of the native and analog molecules using a combination of Fourier transform IR spectroscopy and hydrogen-deuterium (H-D) exchange kinetics. IR spectroscopic results indicate that the analog molecule adopts a gross structure similar to that of the native molecule but significant differences in the conformation of the beta-sheets are observed. Increased bandwidths observed for several of the amide I components also suggest a less rigid structure for the analog molecule. Further, by monitoring the frequency shifts of the individual amide I component bands as a function of hydrogen exchange, we have enhanced our ability to assign these components to individual protein secondary structures, particularly the high frequency beta-strand mode. Hydrogen exchange kinetic studies indicate that the Asp-Arg analog adopts a looser, more flexible solution structure relative to the natural sequence molecule.