SALT-STABILIZED GLOBULAR PROTEIN-STRUCTURE IN 7-M AQUEOUS UREA SOLUTION

A 7 M aqueous urea solution of the 63-residue N-terminal domain of the 334-repressor at pH 7.5 and 18 degrees C contains a mixture of about 10% native, folded protein and 90% unfolded protein. Interconversion b etween the two conformations is slow on the NMR chemical shift time sc ale, so that observation of separate resonances can be used to monitor the equilibrium between folded and unfolded protein when changing the solution conditions. In this paper we describe the influence of vario us salts or non-ionic compounds on this conformational equilibrium. So lution conditions are described which contain a homogenous preparation of the folded protein in the presence of 6 to 7 M urea, providing a b asis for an NMR structure determination in concentrated urea and for s tudies of the solvation of the folded protein in mixed water/urea/salt environments.