Inter-spin distance measurements by PDS.

Shown are experimentally determined distances of spin-labeled proteins and Cα–Cα distances from the Aer2 1–172 crystal structure. The values shown in parentheses refer to the width (Å) at half the maximum peak height, and qualify peak broadening and conformational heterogeneity. Small values represent narrow peaks and a homogeneous conformation. Large values represent broad peaks consistent with more heterogeneous populations.aAttachment of the MTSSL spin labels can add up to 13 Å to the Cα–Cα separation, or equivalently 6.5 Å each.