Fig. 1.

The eNOE principle. a Although conventionally measured NOEs are converted into upper limit distance restraint with a relatively loose tolerance, eNOE-derived restraints have an upper and lower limit. If both NOESY cross peaks caused by a spin pair can be evaluated, the tolerance is very tight (red). If only one cross-peak can be used, the tolerance is somewhat less stringent, in the present application ± 10%. b The eNOE is a time-averaged quantity. For a mobile atom, H₁ sampling positions both close to protons H₂ and H₃, NOEs H₁–H₂ and H₁–H₃ suggest proximity of H₁ to both H₂ and H₃. The combined NOE data can be explained better by a model that allows two states for H₁ shown in red and cyan than by a single-state structure