FIGURE 4.

NMR spectra of EmrE bound to the tetrahedral and planar substrates indicate the same overall protein structure but varying dynamics. A, ¹⁵N/¹H TROSY HSQC spectra of EmrE bound to EtTPP⁺ (magenta), TPP⁺ (black), DPhTPP⁺ (blue), and MBTPP⁺ (green), are similar, with two peaks per residue corresponding to slow exchange of the asymmetric dimer. The assignments for TPP⁺-bound EmrE are displayed for states A (red) and B (black). B, ¹⁵N/¹H TROSY HSQC spectrum of EmrE bound to MeTPP⁺ (red) has a single set of peaks at the average chemical shift, revealing faster conformational exchange of EmrE bound to this ligand than TPP⁺ (black). C, overlay of TPP⁺-bound EmrE (black) with EmrE bound to the two planar ligands, PP²⁺ (DMPC bicelles; orange) and DQ²⁺ (lavender). All spectra were collected identically at pH 7 and 45 °C, with 2-s recycle delay for all ligands except for MeTPP⁺ (6-s recycle delay).