Sub-micromolar pulse dipolar EPR spectroscopy reveals increasing CuII-labelling of double-histidine motifs with lower temperature
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Electron paramagnetic resonance (EPR) distance measurements are making increasingly important contributions to the studies of biomolecules by providing highly accurate geometric constraints. Combining double‐histidine motifs with CuII spin labels can further increase the precision of distance measurements. It is also useful for proteins containing essential cysteines that can interfere with thiol‐specific labelling. However, the non‐covalent CuII coordination approach is vulnerable to low binding‐affinity. Herein, dissociation constants (KD) are investigated directly from the modulation depths of relaxation‐induced dipolar modulation enhancement (RIDME) EPR experiments. This reveals low‐ to sub‐μm CuII KDs under EPR distance measurement conditions at cryogenic temperatures. We show the feasibility of exploiting the double‐histidine motif for EPR applications even at sub‐μm protein concentrations in orthogonally labelled CuII–nitroxide systems using a commercial Q‐band EPR instrument.
Wort , J , Ackermann , K , Giannoulis , A , Stewart , A J , Norman , D & Bode , B E 2019 , ' Sub-micromolar pulse dipolar EPR spectroscopy reveals increasing Cu II -labelling of double-histidine motifs with lower temperature ' , Angewandte Chemie , vol. 131 , no. 34 , pp. 11807-11811 . https://doi.org/10.1002/ange.201904848
Copyright © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
DescriptionJLW is supported by the BBSRC DTP Eastbio. This work was supported by equipment funding through the Wellcome Trust (099149/Z/12/Z) and BBSRC (BB/R013780/1). We gratefully acknowledge ISSF support to the University of St Andrews from The Wellcome Trust.
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