Dynamics and ordering in a spin-labeled oligonucleotide observed by 220 GHz electron paramagnetic resonance.
The dynamics of a newly synthesized cytosine spin-label and the spin-labeled pentamer TTC*TT have been observed by high-frequency (220 GHz) electron paramagnetic resonance (EPR) in aqueous solution at ambient temperature using only nanomolar amounts of spin-label. Temperature studies were carried out for both labeled species in buffer containing glycerol. The motion of the spin-labeled monomer could be fitted using a model of fully anisotropic rotation (FAR) over the entire temperature range studied. In the single-stranded pentamer, the high-field spectra are best interpreted using a model of microscopic ordering with macroscopic disorder (MOMD) with the probe in a highly nonpolar environment. The observed local order parameters of 0.60-0.70 suggest a micelle-like structure in which the label is tightly packed with the hydrophobic bases. These preliminary studies illustrate how the excellent orientation selectivity of high-field EPR provides new dynamic information about local base motions in DNA, and also how high-field EPR of spin-labels allows one to discriminate accurately between the effects of local versus global motions in spin-labeled macromolecules.
Budil
D E
DE
Department of Chemistry, Northeastern University, Boston, Massachusetts 02115, USA. dbudil@neu.edu
Kolaczkowski
S V
SV
Perry
A
A
Varaprasad
C
C
Johnson
F
F
Strauss
P R
PR
D001483:Base Sequence; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D013113:Spin Labels; D013816:Thermodynamics
D009838:Oligodeoxyribonucleotides; D013113:Spin Labels