Figure 8. EPR distance measurements and structure elucidation.

Analysis of protein structure using EPR distance measurements requires triangulation of spin label positions. (A) Triangles represent the least dense labeling strategy that can identify whether a motif is undergoing conformational reorganization. (B) More dense strategies, like quadranges, narrow the possible space that spin label can occupy thereby providing a more detailed description of protein structure and more informative restraints for modeling. (C) To effectively identify positions in three dimensions a pyramid scheme is required.