TY - JOUR TI - Hexameric and pentameric complexes of the ExbBD energizer in the Ton system AU - Maki-Yonekura, Saori AU - Matsuoka, Rei AU - Yamashita, Yoshiki AU - Shimizu, Hirofumi AU - Tanaka, Maiko AU - Iwabuki, Fumie AU - Yonekura, Koji A2 - Grigorieff, Nikolaus VL - 7 PY - 2018 DA - 2018/04/17 SP - e35419 C1 - eLife 2018;7:e35419 DO - 10.7554/eLife.35419 UR - https://doi.org/10.7554/eLife.35419 AB - Gram-negative bacteria import essential nutrients such as iron and vitamin B12 through outer membrane receptors. This process utilizes proton motive force harvested by the Ton system made up of three inner membrane proteins, ExbB, ExbD and TonB. ExbB and ExbD form the proton channel that energizes uptake through TonB. Recently, crystal structures suggest that the ExbB pentamer is the scaffold. Here, we present structures of hexameric complexes of ExbB and ExbD revealed by X-ray crystallography and single particle cryo-EM. Image analysis shows that hexameric and pentameric complexes coexist, with the proportion of hexamer increasing with pH. Channel current measurement and 2D crystallography support the existence and transition of the two oligomeric states in membranes. The hexameric complex consists of six ExbB subunits and three ExbD transmembrane helices enclosed within the central channel. We propose models for activation/inactivation associated with hexamer and pentamer formation and utilization of proton motive force. KW - ExbBD KW - TonB KW - proton motive force KW - energizer KW - cryo-EM KW - X-ray crystallography JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -