INTERACTION OF UREA WITH AN UNFOLDED PROTEIN - THE DNA-BINDING DOMAINOF THE 434-REPRESSOR

Experimental techniques are presented for the observation of the solva tion of the unfolded form of a globular protein, the N-terminal 63-res idue polypeptide from the 434 repressor, in 7 M aqueous urea solution by both water and urea, With the use of N-15-labelled urea it is demon strated that the cross sections through two-dimensional nuclear Overha user enhancement (NOE) spectra at the chemical shifts of H2O and urea both contain direct NOEs with the protein, under conditions where exch ange peaks are observed only in the water cross section, A preliminary analysis of the data showed that the residence times of urea molecule s in solvation sites near the methyl groups of Val, Leu and Ile are si gnificantly longer than those of water molecules in the same sites.