Molecular transport across the bacterial cell enveloppe

• Our team aims to understand the assembly and functioning of two molecular motors present in the envelope of Gram negative bacteria: the Tol and Ton macro-complexes. Both Tol and Ton systems harness the energy produced from the proton motive force generated at the inner membrane to transduce it at the outer membrane. These complexes are involved in functions that are essential for bacterial survival.

  • The Ton system mediates the active uptake across the outer membrane of metal, cyanocobalamin and carbohydrates.

  • The Tol system has a more complex function. Beside its involvement in outer membrane integrity, the system plays a role in the correct localization of some polar factors and chemoreceptors, in outer-membrane phospholipid homeostasis, and in the constriction of the outer membrane during cell division.

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• Both Tol and Ton systems can be parasitized to open a gate for bacteriotoxins (called colicins), which result in bacterial cell death. These systems are also the target of filamentous phages during the infection process, such as the M13 phage targeting E. coli, and the CTX phage which is specific of V. cholerae.

• The Tol and Ton systems share structural homologies, with inner-membrane complexes formed by the TolQ-TolR-TolA and by the ExbB-ExbD-TonB subunits, respectively. In these complexes, the TolA and TonB proteins contain a periplasmic elongated central domain that crosses the periplasm, and interact with outer membrane associated proteins: the TolB/Pal complex and the TonB dependent receptors, respectively.

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• These nano-machines work as molecular motors, converting the electric potential into mechanical energy, using a long-distance energy transduction mechanism, from the inner membrane to proteins located in the outer membrane.