Supplementary Fig. 1: Observing conformational changes in E. coli.

(a) Conformational changes of the second loop was monitored with respect to the seventh loop in the absence (apo) or presence of the ligands (Ca²⁺ and cyanocobalamin, CN–cobalamin). The spin labeled positions are highlighted on the apo-BtuB structure (1NQE). The conformation of the loops as observed in the BtuB–Ca²⁺ (in blue, PDB 1NQG) and BtuB–CN–cobalamin+Ca²⁺ (in yellow, PDB 1NQH) structures are overlaid. The second loop is not resolved in the apo crystal structure. (b, d) Background corrected Q-band PELDOR data for the 188R1–399R1 mutant in E. coli (red) or OM (blue). (c, e) The corresponding distance distributions obtained with Tikhonov regularization. In agreement with the crystal structures, the second loop exhibits large conformational flexibility in the apo-state and binding of the ligands reduce the flexibility. Adapted with permission from ref. ⁴⁸. Joseph, B., Sikora, A. & Cafiso, D. S. Ligand induced conformational changes of a membrane transporter in E. coli cells observed with DEER/PELDOR. J. Am. Chem. Soc. 138, 1844-1847. Copyright (2016) American Chemical Society.