Circular dichroism unfolded proteins, native state

The nature of the unfolded state in denaturant and how it relates to the denatured state under native conditions in the bilayer is a major issue in all denaturation experiments. Thermodynamic arguments from the two-stage model suggest that the relevant denatured state has lost its tertiary structure and maintained the transmembrane helix secondary structure. As noted above, CD spectra on thermally denatured bacteriorhodopsin suggest that the denatured protein maintains most of its helical secondary structure. The extent to which tertiary structure is disrupted is unclear, however. It is possible that some stable interhelical interactions are maintained even at high temperature. The helical secondary structure content is also maintained in SDS micelles, and near-UV circular dichroism (CD) spectra suggest substantial loss or... 

Among the cosolvents, the effects of DMSO on proteins are particularly interesting and diverse. It can play a role as a stabilizer, an activator, a denaturant, an inhibitor, and also as a cryoprotector. Denaturation of proteins induced by DMSO as well as other cosolvents occurs at threshold concentrations where the tertiary and even the secondary structures of proteins are highly disrupted [23]. UV circular dichroism spectral study shows that from 20-25% (v/v) ( 6% mole fraction) DMSO concentration, lysozyme proceeds gradually from its native to the partially unfolded state. This indicates a broad structural transition which is essentially completed by 50% (v/v) (-18% mole fraction) DMSO concentration [24]. 

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