Structure of lysozyme dissolved in neat organic solvents as assessed by NMR and CD spectroscopies

The structure of the model protein hen eggwhite lysozyme dissolved in water and in five neat organic solvents (ethylene glycol, methanol, dimethylsulf oxide (DMSO), formamide, and dimethylformamide (DMF)) has been examined by means of H-1 NMR and circular dichroism (CD) spectroscopies. The NMR spectr a of lysozyme reveal the lack of a defined tertiary structure in all five o rganic solvents, although the examination of line widths suggests the possi bility of some ordered structure in ethylene glycol and in methanol. The ne ar-UV CD spectra of the protein suggest no tertiary structure in lysozyme d issolved in DMSO, formamide, and DMF, while a distinctive (albeit less pron ounced than in water) tertiary structure is seen in ethylene glycol and a d rastically changed one in methanol. A highly developed secondary structure was observed by far-UV CD in ethylene glycol and methanol; interestingly, t he alpha-helix content of the protein in both was greater than in water, wh ile the beta-structure content was lower. (Solvent absorbance in the far-UV region prevents conclusions about the secondary structure in DMSO, formami de and DMF.) (C) 1999 John Wiley & Sons, Inc.