Figure 1.

(A) Comparison of observed and calculated RDCs for the E. coli EI (wild-type) and EI(H189Q) dimers The experimental RDCs for the EI(H189Q) mutant comprise 20 backbone ¹D_NH couplings for each subdomain of EIN (i.e. a total of 40×2 RDCs for the dimer) obtained from a ¹H-¹⁵N TROSY-based ARTSY spectrum¹⁵ with EI(H189Q) aligned in a dilute liquid crystalline medium of pf1 phage¹⁶ (11 mg/ml). For wild-type EI there are 29 ¹D_NH couplings for each subdomain of EIN (i.e. a total of 58×2 RDCs for the dimer).⁹ Top right, wild-type RDCs versus wild-type dimer structure;⁹ top left, EI(H189Q) RDCs versus wild-type EI dimer structure; bottom left, wild-type RDCs versus EI(H189Q) dimer structure (this paper); bottom right, EI(H189Q) RDCs versus EI(H189Q) dimer structure. (B) Comparison of experimental SAXS/WAXS curves (black with gray vertical bars equal to 1 s.d.) recorded for EI(H189Q) with the calculated curves for the final 100 simulated annealing structures in red. The residuals given by $(I_i^{\mathit{calc}}-I_i^{\mathit{obs}})/{\mathit{err}}_i$ are plotted above. The structures were determined by refining against the SAXS/WAXS curve in the range q ≤0.44 Å⁻¹, and the upper end of this range is indicated by the vertical dashed black line. The SAXS/WAXS data were collected at the Advanced Photon Source (Argonne National Laboratory) and processed as described previously.⁹ The SAXS data extend out to q = 0.22 Å⁻¹ and report on interatomic interactions > 28 Å. The SAXS/WAXS data used in refinement (q ≤ 0.44 Å⁻¹) report on interatomic interactions down to 14 Å, and therefore include additional information related to interdomain interactions.