TonB Energiesysteem

How does the ton subcomplex produce energy?

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. In Gram-negative bacteria, outer membrane transporters import nutrients by coupling to an inner membrane protein complex called the Ton complex.

What is a ton system?

At the inner membrane, the Ton system consists of the proton-channel forming complex ExbB-ExbD and the protein TonB, which are together capable of harnessing the PMF. The structure of the whole complex is unknown. Recent cryo-EM data showed two α-helices situated in a periplasm-facing central pore of the pentameric ExbB channel.

What are im Tonb and Om TonB-dependent transporters (tbdts)?

The IM TonB complex and the specific OM TonB-dependent transporters (TBDTs) are used to import scarce and essential nutrients, such as metal sources, vitamin B 12, specific carbohydrates, etc (1, 2).

How many IM proteins are in the TonB complex?

The TonB complex comprises three IM proteins, TonB, ExbB, and ExbD. TonB is the only protein of the complex that directly interacts with the TBDT and thus must be responsible for energy transfer, whereas ExbB and ExbD form a proton channel (3). The structures of the complete TonB complex and the full-length TonB protein are still unknown (4).

What is the relationship between Tonb and tbdt?

Structural data showed that the TonB-TBDT interaction involves a salt bridge between the TonB-box of the transporter and TonB, stabilizing an inter-protein β-sheet (5, 7, 8, 19). Both salt bridge and the inter-protein β-sheet were shown to be important for the energy transfer from the TonB protein to the transporter (30, 31).

What is the structure of A TonB transporter?

Structures of this complex have been described by Wiener and colleagues for BtuB-TonB (77) and by Coulton and colleagues for FhuA-TonB (70). In both structures TonB assumes an alpha-beta fold containing a 3-stranded β-sheet. The TonB box of either transporter adopts a β-strand conformation that pairs with the existing β-sheet of TonB.