Detection of internal and overall dynamics of a two-atom-tethered spin-labeled DNA.
DNA motions consist of several components which couple, making their investigation difficult. This study describes an approach for obtaining dynamical information by EPR when spin-labeled nucleic acids are examined. The analysis is accomplished by implementing two motional models. The first model (i.e., dynamic cylinder model) views the spin-labeled helix as a diffusing cylinder containing internal dynamics which are characterized by an order parameter. The second model (i.e., base disk model) provides correlation times describing the diffusion of the spin-labeled base. In each model, the nitroxide motion consists of both global and internal contributions. Dynamic cylinder and base disk simulations of four duplexes containing nitroxides attached to thymidine by a two-atom tether (DUMTA)-(dT)7DUMTA-(dT)7.(dA)15, [(dT)7DUMTA(dT)7]2.(dA)30, [(dT)7DUMTA(dT)7]3.(dA)45, and [(dT)7DUMTA(dT)7]m.-(dA)n--demonstrate the useful application of this approach. From dynamic cylinder simulations, the order parameter for internal motions is found to be independent of the helix length (S = 0.32 +/- 0.01). Previous base disk simulations of a DNA 26mer and polymer labeled with a five-atom-tethered nitroxide seemed to indicate that tau perpendicular was only sensitive to internal dynamics. Results from base disk simulations of DUMTA-labeled DNA indicate that the perpendicular component of the base disk correlation time (tau perpendicular = 1.4-6.2 ns) is sensitive to global dynamics. Thus, tau perpendicular is a quantitative indicator of both internal and global dynamics. Comparison of the two models reveals that tau perpendicular infinity S2 tau rb, where tau rb represents the rigid-body diffusion of the DNA helix. This relationship between S and tau perpendicular provides a framework for studying conformational changes and size-dependent phenomena in spin-labeled nucleic acids. Application of the dynamic cylinder model to a B-Z transition generates distinct values of S for each of the conformations, indicating that Z-DNA is more rigid than B-DNA.
Keyes
R S
RS
Department of Chemistry, University of Cincinnati, Ohio 45221, USA.
Bobst
A M
AM
D001483:Base Sequence; D003497:Cyclic N-Oxides; D004247:DNA / Q000737:chemistry*; D003857:Deoxyuridine / Q000031:analogs & derivatives; D004578:Electron Spin Resonance Spectroscopy; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D013113:Spin Labels; D013816:Thermodynamics
D003497:Cyclic N-Oxides; D009838:Oligodeoxyribonucleotides; D013113:Spin Labels; C070254:5-(((2,2,6,6-tetramethyl-1-oxy-4-piperidyl)amino)methyl)-2'-deoxyuridine; D004247:DNA; D003857:Deoxyuridine