Site-Directed Spin Labeling for EPR Studies of Nucleic Acids

Abstract

Electron paramagnetic resonance (EPR) spectroscopy has emerged as a valuable technique to study the structure and dynamics of nucleic acids and their complexes with other biomolecules. EPR studies require incorporation of stable free radicals (spin labels), usually aminoxyl radicals (nitroxides), at specific sites in the nucleic acids using site-directed spin labeling (SDSL). In addition to the advancement of EPR instrumentation and pulsed EPR techniques, new strategies for SDSL have emerged, in particular, use of click chemistry, biopolymer catalysis, and noncovalent labeling. Furthermore, tailor-made spin labels with improved stability and spectroscopic properties have evolved, such as rigid spin labels that allow determination of accurate distances in addition to orientations between two spin labels. This chapter gives an overview of nucleic acids spin labeling using the three main strategies of SDSL, namely spin labeling during oligonucleotide synthesis, post-synthetic-, and noncovalent labeling. The spin-labeling methods have been categorized according to the labeling site.