Extended Data Fig. 10: TonB recruitment to the ExbBD complex.
From: Structures of the stator complex that drives rotation of the bacterial flagellum
a, SEC-MALS profile of purified Pseudomonas TonB-ExbBD (black curve; absorbance at 280 nm (A280)) and ExbBD (grey curve; absorbance at 280 nm (A280)) with SDS-PAGE analysis of each sample inlayed. Total protein-detergent complex molar mass (green) and deconvoluted protein (blue) and detergent (orange) molar masses are shown. A ~30 kDa difference in molar mass is observed between the complexes consistent with the TonB-ExbBD complex containing one TonB subunit. Similar data were obtained from three independent purifications. b, Evolutionary co-variation of residues between TonB and ExbB displayed on the E. coli ExbBD coordinates37 (PDB 6tyi). For clarity, a topological model of the TMH of TonB is shown in orange with TonB-ExbB contacts indicated as dashed lines. ExbB residues that coevolve with TonB decorate the external surface of ExbB and are displayed in green. ExbB (grey) and ExbD (blue) are displayed as ribbon cartoons. Contacts shown were generated by Gremlin6 and have a probability score of > 0.9. c, inspection of the cryo-em volume derived from the ExbBDTonB sample, prior to post-processing, at a low contour level reveals a single, tube of density, consistent with the predicted location of the TonB transmembrane helix running across the exterior of a single copy of ExbB. Although likely at a low occupancy c.f. the other components, we tentatively assign this as TonB.
