Fig. 1

Pulse sequences used in DEER, DQC, and RIDME experiments

Fig. 2

Schematic illustration of pulsed dipolar EPR experiments. (a) Relative positions of pump and observer pulses in a DEER experiment; (b) Pulse position in DQC and RIDME experiments; (c) Geometry representation of a coupled electron spin pair, where θ denotes the angle between the inter-spin vector$\overrightarrow{r}$and the external magnetic field$\overrightarrow{B0}$; (d) Background-corrected time trace, modulation depth λ and maximum dipolar evolution time tmax obtained from a DEER experiment

Table 1

Correspondence between interspin distance r and maximum dipolar evolution time tmax

Table 2

Comparison of three PD-EPR techniques

Fig. 3

Chemical structures of representative spin labels commonly used in PD-EPR experiments, in which the reactive moiety for protein modification was highlighted in yellow

Fig. 4

Schematic illustration of general strategies for site-specific modification of proteins with spin labels

Fig. 5

Scheme of structural variations determined by PD-EPR measurements. This distance distribution measured by PD-EPR between two spin labels attached to a biomacromolecule, and the gray shading area represents the range of spin label relocations under different conditions. The PD-EPR technique measures the spin distance distribution function P(r). By comparing the changes in the distance distribution, it allows the study of conformational changes in biomolecules