Selective DMSO-induced conformational changes in proteins from Raman optical activity

Abstract

The function of a protein is determined by its structure, which is intrinsically related to its solvent environment. Based on this paradigm, there has been a great deal of interest in the role that non-aqueous solvents play in regulating protein structure, with some debate in the literature regarding dimethyl sulfoxide (DMSO). Thus, in this work we have used Raman and Raman optical activity (ROA) spectroscopies to investigate conclusively the changes induced by DMSO in the secondary structure of an array of proteins including human serum albumin (highly α-helical), bovine α-lactalbumin (mainly α-helical), bovine ribonuclease A (containing both α-helix and β-sheet), bovine β-lactoglobulin (mainly β-sheet), and bovine α-casein (disordered). Our results clearly demonstrate that 100% DMSO solutions destabilize α-helices completely, converting them into the poly(L-proline) II (PPII) helix conformation. However, low concentrations of DMSO (10% v/v) were found to have little effect on the structure of even the most helical protein, human serum albumin. In the case of α-casein, the natively unfolded protein rich in PPII helix was converted into a further disordered structure when dissolved in pure DMSO. By contrast, β-sheets remained mostly unaffected regardless of DMSO concentration. While providing new insights into protein structure in organic solvents, this work reinforces the capability of vibrational optical activity to assess conformations of biomolecules in conditions not accessible to other techniques, such as X-ray crystallography and NMR.

Optically Active Vibrational Spectroscopy of α‐Aminoisobutyric Acid Foldamers in Organic Solvents and Phospholipid Bilayers

“…The ROA spectrum of ( S )‐ 7 (Cbz( l ‐Phe)Aib 4 O t Bu, M helix) shows very weak positively signed peaks at 1664 and 1710 cm −1 , with a stronger negatively signed peak at 1689 cm −1 , while foldamer ( R )‐ 7 (Cbz( d ‐Phe)Aib 4 O t Bu, P helix) produces the mirror image (very weak negatively signed peaks at 1664 cm −1 and ≈1720 cm −1 , with a stronger positively signed peak at 1689 cm −1 ). The band at 1668 cm −1 has been assigned to peptides in a 3 10 ‐helical conformation, whereas the peak at 1689 cm −1 may arise from disordered secondary structures . The amide I band for ( S )‐ 7 and ( R )‐ 7 appears distinct from an α‐helix (right‐handed) marker band, which is represented by a broad couplet that is negative at ≈1640 cm −1 and positive at ≈1665 cm −1 .…”

Investigation of DMSO‐Induced Conformational Transitions in Human Serum Albumin Using Two‐Dimensional Raman Optical Activity Spectroscopy

“…Accordingly, these variations in the amide III region are followed by changes in the amide I region, with the α‐helix couplet being replaced with a positive band of lower intensity and shifted to higher wavenumbers . Altogether, these spectral signatures corroborate the conversion of α‐helix into PPII conformation in DMSO solution as described before . It is important to mention, however, that a recent study by Dzwolak et al suggests that the ROA band at ~1310 cm ‐1 may result from transfer of chirality from the protein to the otherwise ROA‐silent solvent.…”

Catalytic activity and structural stability of three different Bacillus enzymes in water/organic co-solvent mixtures

“…Among the remaining co-solvents, the least harmful to the catalytic functions of BlGGT, BsAPII, and BlALDH was DMSO, followed by methanol and ethanol. DMSO at low concentrations (<10 %, v/v) has been shown to stabilize some protein samples [26][27][28]. Although the protective mechanism of DMSO remains obscure, protein-solvent preferential interactions may explain its beneficial effect on the conformational stability of proteins in aqueous solutions [27,29].…”