August 2011

Document Type


Degree Name



Dept. of Molecular Microbiology and Immunology


Oregon Health & Science University


The ability to scavenge and transport iron from the environment and inside the vertebrate host is essential for survival of most bacterial species. The TonB-ExbB-ExbD energy transduction system is conserved through many Gram-negative species and is used to transduce energy from the proton motive force (PMF) in the inner-membrane to the outer-membrane iron-siderophore transporters. Unlike E. coli, the Vibrio species have multiple TonB systems. In these bacteria, the TonB2 systems also include a fourth protein, TtpC that is essential for energy transduction and iron transport. The TtpC proteins are highly conserved yet display specificity towards certain outer-membrane transporters – suggesting that the TtpC protein, in conjunction with, or in place of TonB2, could be transducing the energy to the outer-membrane transporters. Most TonB proteins contain a conserved SxxxH motif that is involved in converting the energy of the PMF to conformational changes in the TonB periplasmic domain. The SxxxH motif does not exist in the vibrio TonB2 proteins, but is instead found in the vibrio TtpC proteins. The conserved histidine is essential for Fe-ferrichrome transport in V. cholerae and supports the hypothesis that TtpC is the energy-transducing protein in the vibrio TonB2 energy transduction systems. The discovery of a fourth component to the TonB2 system is of significant interest because it suggests a variation or unique mechanism that is used by marine organisms to transduce energy to the outer membrane receptor proteins. Although the vibrio TonB2 systems are similar in organization and protein homology to other Gramnegative TonB systems, the addition of the TtpC protein, and the proof of its essentiality presented here indicate a more complex mechanism of energy transduction present in the periplasm of the Vibrio species.




School of Medicine



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