On the DMSO-dissolved state of insulin : a vibrational spectroscopic study of structural disorder
Faculty of Sciences. Chemistry
The journal of physical chemistry : B : condensed matter, materials, surfaces, interfaces and biophysical. - Washington, D.C.
, p. 11863-11871
Upon dissolving in dimethyl sulfoxide (DMSO), native insulin and insulin amyloid fibrils convert into an identical disordered structural state based on IR spectral characteristics. Here, we investigate the DMSO-denatured state of insulin using a number of spectroscopic methods: near-UV circular dichroism, infrared absorption spectroscopy, vibrational circular dichroism (VCD), Raman scattering, and Raman optical activity (ROA), as well as by carrying out 140-ns-long molecular dynamics (MD) simulations of DMSO-dissolved native insulin monomers. According to this work, the DMSO-solvated state of insulin is an ensemble of conformations including polyproline II-type helix and possibly a residual a-helical structure. Effects of DMSO-specific solvation and conformation-restricting covalent structure of insulin (including the three intact disulfide bridges) are argued to play important roles in stabilizing the disordered state of the protein. A comparison of ROA spectra of insulin dissolved in fully deuterated and nondeuterated DMSO suggested transfer of chirality from the protein to the otherwise ROA-silent solvent. Our study provides an example of a biological protein that acquires a substantial population of PP II conformation in an entirely nonaqueous environment. The DMSO-unfolded state of insulin and its dynamics are also discussed in the context of the established link between PP II conformation and protein misfolding.