A general model to optimise CuII labelling efficiency of double-histidine motifs for pulse dipolar EPR applications

Joshua L. Wort, Katrin Ackermann, David G. Norman, Bela E. Bode (Lead / Corresponding author)

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Abstract

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 dH 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, depending upon 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.

Original languageEnglish
Pages (from-to)3810-3819
Number of pages10
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number6
Early online date27 Jan 2021
DOIs
Publication statusPublished - 14 Feb 2021

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