Open AccessSolvent dielectric effects on protein dynamics.
Author(s) -
Rhett Affleck,
Charles A. Haynes,
Douglas S. Clark
Publication year - 1992
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.89.11.5167
Subject(s) - electron paramagnetic resonance , dielectric , chemistry , solvent , molecular dynamics , spin label , protein dynamics , chemical physics , solvent effects , resonance (particle physics) , computational chemistry , crystallography , analytical chemistry (journal) , nuclear magnetic resonance , organic chemistry , materials science , atomic physics , physics , optoelectronics
Electron paramagnetic resonance (EPR) spectroscopy and molecular dynamics (MD) simulations were used to investigate the dynamics of alpha-chymotrypsin in solvents ranging in dielectric constant from 72 to 1.9. EPR measurements showed that motions in the vicinity of two spin-labeled amino acids (Met-192 and Ser-195) decreased dramatically with decreasing solvent dielectric constant, a trend consistent with changes in the electrostatic force between charged residues of the protein. EPR results and MD simulations revealed a very similar functional dependence between rates of motion in the protein and the dielectric constant of the bulk solvent; however, predicted motions of protein atoms were markedly faster than measured motions of the spin labels. MD calculations for dielectric constants of 5 and 72 showed the greatest differences near the outer surface of the protein. In general, at the lower dielectric constant many atoms of the protein move more slowly, and many of the slowest residues are near the exterior. These results suggest that altered dynamics may contribute to the unusual properties--e.g., modified stereoselectivities--of enzymes in nearly dry organic solvents.