Structural Insight into the Role of the Ton Complex in Energy Transduction

Overview

Journal Nature

Specialty Science

Date 2016 Sep 23

PMID 27654919

Citations 72

Authors

Herve Celia

Nicholas Noinaj

Stanislav D Zakharov

Enrica Bordignon

Istvan Botos

Monica Santamaria

Travis J Barnard

William A Cramer

Roland Lloubes

Susan K Buchanan

Affiliations

Soon will be listed here.

Abstract

In Gram-negative bacteria, outer membrane transporters import nutrients by coupling to an inner membrane protein complex called the Ton complex. The Ton complex consists of TonB, ExbB, and ExbD, and uses the proton motive force at the inner membrane to transduce energy to the outer membrane via TonB. Here, we structurally characterize the Ton complex from Escherichia coli using X-ray crystallography, electron microscopy, double electron-electron resonance (DEER) spectroscopy, and crosslinking. Our results reveal a stoichiometry consisting of a pentamer of ExbB, a dimer of ExbD, and at least one TonB. Electrophysiology studies show that the Ton subcomplex forms pH-sensitive cation-selective channels and provide insight into the mechanism by which it may harness the proton motive force to produce energy.

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References

Ollis A, Kumar A, Postle K . The ExbD periplasmic domain contains distinct functional regions for two stages in TonB energization. J Bacteriol. 2012; 194(12):3069-77. PMC: 3370882. DOI: 10.1128/JB.00015-12. View

Kojima S, Blair D . Conformational change in the stator of the bacterial flagellar motor. Biochemistry. 2001; 40(43):13041-50. DOI: 10.1021/bi011263o. View

von Hagens T, Polyhach Y, Sajid M, Godt A, Jeschke G . Suppression of ghost distances in multiple-spin double electron-electron resonance. Phys Chem Chem Phys. 2013; 15(16):5854-66. DOI: 10.1039/c3cp44462g. View

Braun V . The structurally related exbB and tolQ genes are interchangeable in conferring tonB-dependent colicin, bacteriophage, and albomycin sensitivity. J Bacteriol. 1989; 171(11):6387-90. PMC: 210519. DOI: 10.1128/jb.171.11.6387-6390.1989. View

Mueller P, RUDIN D, Tien H, WESCOTT W . Reconstitution of cell membrane structure in vitro and its transformation into an excitable system. Nature. 1962; 194:979-80. DOI: 10.1038/194979a0. View

Bassford Jr P, Bradbeer C, Kadner R, Schnaitman C . Transport of vitamin B12 in tonB mutants of Escherichia coli. J Bacteriol. 1976; 128(1):242-7. PMC: 232849. DOI: 10.1128/jb.128.1.242-247.1976. View

Krissinel E, Henrick K . Inference of macromolecular assemblies from crystalline state. J Mol Biol. 2007; 372(3):774-97. DOI: 10.1016/j.jmb.2007.05.022. View

Zhai Y, Heijne W, Saier Jr M . Molecular modeling of the bacterial outer membrane receptor energizer, ExbBD/TonB, based on homology with the flagellar motor, MotAB. Biochim Biophys Acta. 2003; 1614(2):201-10. DOI: 10.1016/s0005-2736(03)00176-7. View

Noinaj N, Guillier M, Barnard T, Buchanan S . TonB-dependent transporters: regulation, structure, and function. Annu Rev Microbiol. 2010; 64:43-60. PMC: 3108441. DOI: 10.1146/annurev.micro.112408.134247. View

10.

Ollis A, Postle K . ExbD mutants define initial stages in TonB energization. J Mol Biol. 2011; 415(2):237-47. PMC: 3258360. DOI: 10.1016/j.jmb.2011.11.005. View

11.

Polyhach Y, Bordignon E, Jeschke G . Rotamer libraries of spin labelled cysteines for protein studies. Phys Chem Chem Phys. 2010; 13(6):2356-66. DOI: 10.1039/c0cp01865a. View

12.

Ollis A, Manning M, Held K, Postle K . Cytoplasmic membrane protonmotive force energizes periplasmic interactions between ExbD and TonB. Mol Microbiol. 2009; 73(3):466-81. PMC: 2729267. DOI: 10.1111/j.1365-2958.2009.06785.x. View

13.

Brewer S, Tolley M, Trayer I, BARR G, Dorman C, Hannavy K . Structure and function of X-Pro dipeptide repeats in the TonB proteins of Salmonella typhimurium and Escherichia coli. J Mol Biol. 1990; 216(4):883-95. DOI: 10.1016/S0022-2836(99)80008-4. View

14.

Sverzhinsky A, Fabre L, Cottreau A, Biot-Pelletier D, Khalil S, Bostina M . Coordinated rearrangements between cytoplasmic and periplasmic domains of the membrane protein complex ExbB-ExbD of Escherichia coli. Structure. 2014; 22(5):791-7. DOI: 10.1016/j.str.2014.02.010. View

15.

Smart O, Neduvelil J, Wang X, Wallace B, Sansom M . HOLE: a program for the analysis of the pore dimensions of ion channel structural models. J Mol Graph. 1996; 14(6):354-60, 376. DOI: 10.1016/s0263-7855(97)00009-x. View

16.

Kodding J, Killig F, Polzer P, Howard S, Diederichs K, Welte W . Crystal structure of a 92-residue C-terminal fragment of TonB from Escherichia coli reveals significant conformational changes compared to structures of smaller TonB fragments. J Biol Chem. 2004; 280(4):3022-8. DOI: 10.1074/jbc.M411155200. View

17.

Cascales E, Lloubes R, Sturgis J . The TolQ-TolR proteins energize TolA and share homologies with the flagellar motor proteins MotA-MotB. Mol Microbiol. 2001; 42(3):795-807. DOI: 10.1046/j.1365-2958.2001.02673.x. View

18.

Clement E, Mesini P, Pattus F, Schalk I . The binding mechanism of pyoverdin with the outer membrane receptor FpvA in Pseudomonas aeruginosa is dependent on its iron-loaded status. Biochemistry. 2004; 43(24):7954-65. DOI: 10.1021/bi049768c. View

19.

Higgs P, Larsen R, Postle K . Quantification of known components of the Escherichia coli TonB energy transduction system: TonB, ExbB, ExbD and FepA. Mol Microbiol. 2002; 44(1):271-81. DOI: 10.1046/j.1365-2958.2002.02880.x. View

20.

Pettersen E, Goddard T, Huang C, Couch G, Greenblatt D, Meng E . UCSF Chimera--a visualization system for exploratory research and analysis. J Comput Chem. 2004; 25(13):1605-12. DOI: 10.1002/jcc.20084. View