TonB

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Template:STRUCTURE 1xx3

Contents

Structure

The structure to the right (1XX3) shows the structure of TonB. The protein spans the periplasm [1], with the C-terminus of TonB spanning from residues ~150 to 239[2].

Function

TonB is involved in the uptake of iron as a component of the TonB/ExbB/ExbD complex of the Ton system. It's activity is determined by the presence of ExbB and ExbD[3]. The C-terminus of TonB interacts with outer membrane transporters, known as TonB-dependent outer membrane transporters (TBDTs)[4], allowing the translocation of biochemical molecules between the inner and outer membrane[2].

Interaction with ExbB/ExbD

TonB and ExbD bind to ExbB in a protein complex that prevents the degradation of the TonB protein. TonB and ExbD are anchored to the cytoplasmic membrane via their N-terminal hydrophobic sequences, with the rest of the protein complex extending into the periplasmic space, allowing for interaction with outer membrane proteins.[3]

BtuB-TonB Complex

As shown in the 3D structure to the right (2GSK), TonB complexes with BtuB in order to aid the transport of nutrients such as cobalamins[5] across the outer membrane by incorporating the proton-motive force into the outer membrane.[6] TonB attaches to BtuB on the periplasmic side of the 614 amino acid BtuB protein[6].

Template:STRUCTURE 2gsk

References

  1. ↑ Pawelek PD, Croteau N, Ng-Thow-Hing C, Khursigara CM, Moiseeva N, Allaire M, Coulton JW. Structure of TonB in complex with FhuA, E. coli outer membrane receptor. Science. 2006 Jun 2;312(5778):1399-402. PMID:16741125 doi:312/5778/1399
  2. ↑ 2.0 2.1 Postle K, Kastead KA, Gresock MG, Ghosh J, Swayne CD. The TonB Dimeric Crystal Structures Do Not Exist In Vivo. MBio. 2010 Dec 21;1(5). pii: e00307-10. PMID:21179522 doi:10.1128/mBio.00307-10
  3. ↑ 3.0 3.1 Kampfenkel K, Braun V. Topology of the ExbB protein in the cytoplasmic membrane of Escherichia coli. J Biol Chem. 1993 Mar 15;268(8):6050-7. PMID:8449962
  4. ↑ Wiener MC. TonB-dependent outer membrane transport: going for Baroque? Curr Opin Struct Biol. 2005 Aug;15(4):394-400. PMID:16039843 doi:10.1016/j.sbi.2005.07.001
  5. ↑ Cadieux N, Bradbeer C, Kadner RJ. Sequence changes in the ton box region of BtuB affect its transport activities and interaction with TonB protein. J Bacteriol. 2000 Nov;182(21):5954-61. PMID:11029413
  6. ↑ 6.0 6.1 Shultis DD, Purdy MD, Banchs CN, Wiener MC. Outer membrane active transport: structure of the BtuB:TonB complex. Science. 2006 Jun 2;312(5778):1396-9. PMID:16741124 doi:312/5778/1396

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