title: On the DMSO-dissolved state of insulin: a vibrational spectroscopic study of structural disorder.
abstract: 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 α-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.
authors.affiliation: Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland. wdzwolak@chem.uw.edu.pl
authors.forename: Wojciech
authors.initials: W
authors.lastname: Dzwolak
authors.forename: Jarosław
authors.initials: J
authors.lastname: Kalinowski
authors.forename: Christian
authors.initials: C
authors.lastname: Johannessen
authors.forename: Viktoria
authors.initials: V
authors.lastname: Babenko
authors.forename: Ge
authors.initials: G
authors.lastname: Zhang
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Keiderling
mesh_terms: D000818:Animals; D002417:Cattle; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D007328:Insulin / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D017433:Protein Structure, Secondary; D012996:Solutions; D013057:Spectrum Analysis; D014732:Vibration
chemical_list: D007328:Insulin; D012996:Solutions; D004121:Dimethyl Sulfoxide