A structure-based simulation approach for electron paramagnetic resonance spectra using molecular and stochastic dynamics simulations.
Electron paramagnetic resonance (EPR) spectroscopy using site-directed spin-labeling is an appropriate technique to analyze the structure and dynamics of flexible protein regions as well as protein-protein interactions under native conditions. The analysis of a set of protein mutants with consecutive spin-label positions leads to the identification of secondary and tertiary structure elements. In the first place, continuous-wave EPR spectra reflect the motional freedom of the spin-label specifically linked to a desired site within the protein. EPR spectra calculations based on molecular dynamics (MD) and stochastic dynamics simulations facilitate verification or refinement of predicted computer-aided models of local protein conformations. The presented spectra simulation algorithm implies a specialized in vacuo MD simulation at 600 K with additional restrictions to sample the entire accessible space of the bound spin-label without large temporal effort. It is shown that the distribution of spin-label orientations obtained from such MD simulations at 600 K agrees well with the extrapolated motion behavior during a long timescale MD at 300 K with explicit water. The following potential-dependent stochastic dynamics simulation combines the MD data about the site-specific orientation probabilities of the spin-label with a realistic rotational diffusion coefficient yielding a set of trajectories, each more than 700 ns long, essential to calculate the EPR spectrum. Analyses of a structural model of the loop between helices E and F of bacteriorhodopsin are illustrated to demonstrate the applicability and potentials of the reported simulation approach. Furthermore, effects on the motional freedom of bound spin-labels induced by solubilization of bacteriorhodopsin with Triton X-100 are examined.
Beier
Christian
C
Fachbereich Physik, Universität Osnabrück, Osnabrück, Germany.
Steinhoff
Heinz-Jürgen
HJ
D000465:Algorithms; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D009154:Mutation; D017830:Octoxynol / Q000737:chemistry; D013113:Spin Labels; D013269:Stochastic Processes
D013113:Spin Labels; D001436:Bacteriorhodopsins; D017830:Octoxynol