Dimethyl sulfoxide binding to globular proteins: A nuclear magnetic relaxation dispersion study

The 2 H magnetic relaxation dispersion (NMRD) technique was used to characterize interactions of dimethyl sulfoxide (DMSO) with globular proteins. A difference NMRD experiment involving the N‐acetylglucosamine trisaccharide inhibitor, demonstrated that the DMSO 2 H NMRD profile in lysozyme solution is due to a single DMSO molecule bound in the active cleft, with a molecular order parameter of 0.47 + 0.05 and a residence time in the range 10 ns to 5 ms. With the aid of transverse 2 H relaxation data, the upper bound of the residence time was further reduced to 100 μs. A 1 H shift titration experiment was also performed, yielding a binding constant of 2.3 + 0.3 M −1 at 27 °C. In contrast to lysozyme, no DMSO dispersion was observed for bovine pancreatic trypsin inhibitor (BPTI), indicating that a stable DMSO‐protein complex requires a cleft of appropriate geometry in addition to hydrogen‐bond and hydrophobic interactions.