Abstract
Pulse electron paramagnetic resonance (EPR) is gaining increasing importance in structural biology. The PELDOR (pulsed electron–electron double resonance) method allows extracting distance information on the nanometer scale. Here, we demonstrate the efficient extraction of distances from multimeric systems such as membrane‐embedded ion channels where data analysis is commonly hindered by multi‐spin effects.
Highlights
Nanometer distance restraints obtained through electron paramagnetic resonance (EPR) have attracted increasing attention in structural biology.[1]
This introduces an additional challenge for EPR distance measurements, as extracting all distances present in such multiply labeled nano-objects is complicated by multi-spin contributions to the dipolar coupling.[7]
The 4-pulse PELDOR experiment is mostly used for distance measurements.[8]
Summary
Nanometer distance restraints obtained through electron paramagnetic resonance (EPR) have attracted increasing attention in structural biology.[1]. While a regularization artifact and improper amplitudes in the distance distribution of a tetraradical were attributed to multi-spin effects,[9] Jeschke et al provided the first systematic study using three-spin model systems and relieving the problem by reducing the probability of multiple excitation.[7] Similar experiments had been proposed for determining the numbers of interacting monomeric units[10] and had shown some improvement in applications on albumin.[11] Explicit treatment of multi-spin effects allowed quantitative simulations in tetrameric KcsA.[12] Further recent applications include the heptameric mechanosensitive channel of small conductance (MscS)[13] and the octameric outer membrane protein Wza from E.coli.[14] In both cases only the modal distances (between one monomer and the in rotational symmetry) were interpreted.
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