High populations of non-native structures in the denatured state are compatible with the formation of the native folded state

The structures of the denatured states of the spectrin SH3 domain and a mut ant designed to have a non-native helical tendency at the N terminus have b een analyzed under mild acidic denaturing conditions by nuclear magnetic re sonance methods with improved resolution. The wild-type denatured state has little residual structure. However, the denatured state of the mutant has an approximately 50% populated helical structure from residues 2 to 14, a r egion that forms part of the beta-sheet structure in the folded state. Comp arison with a peptide corresponding to the same sequence shows that the hel ix is stabilized in the whole domain, likely by non-local interactions with other parts of the protein as suggested by changes in a region far from th e mutated sequence. These results demonstrate that high populations of-non- native secondary structure elements in the denatured state are compatible w ith the formation of the native folded structure. (C) 1998 Academic Press.