A Gadolinium Spin Label with Both a Narrow Central Transition and Short Tether for Use in Double Electron Electron Resonance Distance Measurements

• Published in: Inorganic chemistry Vol. 58; no. 5; pp. 3015 - 3025
• Main Authors: Shah, Anokhi, Roux, Amandine, Starck, Matthieu, Mosely, Jackie A, Stevens, Michael, Norman, David G, Hunter, Robert I, El Mkami, Hassane, Smith, Graham M, Parker, David, Lovett, Janet E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04-03-2019
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b02892

The design, synthesis, and application of a nine-coordinate gadolinium­(III)-containing spin label, [Gd.sTPATCN]-SL, for use in nanometer-distance measurement experiments by EPR spectroscopy is presented. The spin label links to cysteines via a short thioether tether and has a narrow central transition indicative of small zero-field splitting (ZFS). A protein homodimer, TRIM25cc, was selectively labeled with [Gd.sTPATCN]-SL (70%) and a nitroxide (30%) under mild conditions and measured using the double electron electron resonance (DEER) technique with both commercial Q-band and home-built W-band spectrometers. The label shows great promise for increasing the sensitivity of DEER measurements through both its favorable relaxation parameters and the large DEER modulation depth at both Q- and W-band for the inter-Gd­(III) DEER measurement which, at 9%, is the largest recorded under these conditions.