Native-like secondary structure of molten globules.

The most common evidence for the existence of secondary structure in a globular protein is the presence of a strongly pronounced far-UV circular dichroism (CD) spectrum. Although CD spectra of native proteins are well described and their quantitative analysis is widely used, similar studies for denatured proteins have still to be done. Far-UV CD spectra of nine proteins in the native and the pH-induced molten globule states were acquired and analyzed. Singular value decomposition showed that the spectra of molten globules could be described as a superposition of at least three independent components (most likely alpha-, beta- and irregular structure). A self-consistent procedure of CD spectra analysis revealed the existence of a clear correlation between the shape of the molten globule spectra and the content of secondary structure elements in the corresponding native proteins, as determined from X-ray data. A mathematical expression of this correlation in terms of the Pierson coefficient amounts to the value of 0.9 for both the alpha-helix and the beta-structure. Thus, the secondary structure of proteins in the molten globule state is close to that in the native state.