Orthogonal spin labeling using click chemistry for in vitro and in vivo applications

• Published in: Journal of magnetic resonance (1997) Vol. 275; pp. 38 - 45
• Main Authors: Kucher, Svetlana, Korneev, Sergei, Tyagi, Swati, Apfelbaum, Ronja, Grohmann, Dina, Lemke, Edward A., Klare, Johann P., Steinhoff, Heinz-Jürgen, Klose, Daniel
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2017
• Subjects: Alkynes - chemistry; Azides - chemistry; Catalysis; Click chemistry; Click Chemistry - methods; Copper - chemistry; Cycloaddition Reaction; Cysteine - chemistry; DEER; Electron Spin Resonance Spectroscopy - methods; EPR spectroscopy; In vivo EPR; Kinetics; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Conformation; Nitrogen Oxides - chemistry; Orthogonal labeling; Site-directed spin labeling; Spin Labels - chemical synthesis; Site-directed spin labeling; DEER; In vivo EPR; Click chemistry; Orthogonal labeling; EPR spectroscopy
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2016.12.001

[Display omitted] •Site-directed spin labeling of unnatural amino acids in proteins by click chemistry.•Quantitative labeling yields within incubation times as short as 30min.•Orthogonal labeling approach independent of cysteines.•Evaluation of Cu-free- and Cu-catalyzed reaction variants.•Suitable coupling chemistry for spin labeling in vivo. Site-directed spin labeling for EPR- and NMR spectroscopy has mainly been achieved exploiting the specific reactivity of cysteines. For proteins with native cysteines or for in vivo applications, an alternative coupling strategy is required. In these cases click chemistry offers major benefits by providing a fast and highly selective, biocompatible reaction between azide and alkyne groups. Here, we establish click chemistry as a tool to target unnatural amino acids in vitro and in vivo using azide- and alkyne-functionalized spin labels. The approach is compatible with a variety of labels including reduction-sensitive nitroxides. Comparing spin labeling efficiencies from the copper-free with the strongly reducing copper(I)-catalyzed azide-alkyne click reaction, we find that the faster kinetics for the catalyzed reaction outrun reduction of the labile nitroxide spin labels and allow quantitative labeling yields within short reaction times. Inter-spin distance measurements demonstrate that the novel side chain is suitable for paramagnetic NMR- or EPR-based conformational studies of macromolecular complexes.