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A General Model to Optimise Copper(II) Labelling Efficiency of Double-Histidine Motifs for Pulse Dipolar EPR Applications

preprint
revised on 27.11.2020, 12:35 and posted on 30.11.2020, 06:07 by Joshua L. Wort, Katrin Ackermann, David G. Norman, Bela E. Bode

Electron paramagnetic resonance (EPR) distance measurements are making increasingly important contributions to studies of biomolecules underpinning health and disease by providing highly accurate and precise geometric constraints. Combining double-histidine (dH) motifs with CuII spin labels shows promise for further increasing the precision of distance measurements, and for investigating subtle conformational changes. However, non-covalent coordination-based spin labelling is vulnerable to low binding affinity. Dissociation constants of dH motifs for CuII-nitrilotriacetic acid were previously investigated via relaxation induced dipolar modulation enhancement (RIDME), and demonstrated the feasibility of exploiting the double histidine motif for EPR applications at sub-μM protein concentrations. Herein, the feasibility of using modulation depth quantitation in CuII-CuII RIDME to simultaneously estimate a pair of non-identical independent KD values in such a tetra-histidine model protein is addressed. Furthermore, we develop a general speciation model to optimise CuII labelling efficiency, in dependence of pairs of identical or disparate KD values and total CuII label concentration. We find the dissociation constant estimates are in excellent agreement with previously determined values, and empirical modulation depths support the proposed model.


Funding

BBSRC DTP Eastbio

Wellcome Trust (099149/Z/12/Z

BBSRC (BB/R013780/1)

ISSF support to the University of St Andrews from the Wellcome Trust

History

Email Address of Submitting Author

beb2@st-andrews.ac.uk

Institution

University of St Andrews

Country

United Kingdom

ORCID For Submitting Author

0000-0002-3384-271X

Declaration of Conflict of Interest

None to declare

Exports