PROSITE documentation PDOC52015
TonB C-terminal domain profile


The cell wall of Gram-negative bacteria consists of two lipid bilayers, the outer membrane (OM) and the cytoplasmic membrane (CM) with the peptidoglycan layer in between. The OM protects Gram-negative bacteria from environmental hazards such as antibiotics and detergents. At the same time, Gram-negative bacteria require rare essential nutrients such as iron, vitamins that are present in the extracellular environment at very low concentrations. Gram-negative bacteria have evolved active acquisition systems to pass the essential nutrients through OM and CM. Since there is no electrochemical gradient to power the active transport at the OM and no ATP in the periplasmic space, these transporters must extract energy from the CM. These transporters in the OM are termed TonB-dependent transporters (TBDTs) (see <PDOC00354>) because they presumably extract the energy from the proton-motive force (pmf) of the CM via the trans-periplasmic protein, TonB protein. Whereas generally a single TonB protein allows the acquisition of several nutrients through their cognate receptor, in some species one particular TonB is dedicated to a specific system. TonB is generally found in complex with the ExbB and ExbD proteins, located in the cytoplasmic membrane. ExbB and ExbD are accessory proteins anchored in the CM that convey the pmf across the CM to TonB. TonB protein mediates the energy transduction from the CM to TBDTs. TonB has an N-terminal transmembrane (TM) domain anchored in the CM. The TM domain is followed by the central region mostly consisting of Pro-Glu and Pro-Lys repeats. Extended conformation of the central region allows the protein to span the periplasmic space between OM and CM. The C-terminal domain (CTD) of TonB protein has a globular structure of ~100 residues and interacts with a conserved TonB box motif located at the N-terminus of TBDTs, which likely induces structural changes in the OM transporters (see <PDOC00354>) [1,2,3,4].

The TonB C-terminal domain is composed of a mixed α/β structure that contains three β-strands and one α-helix (see <PDB:1XX3>) [1,2,3,4].

The profile we developed covers the entire TonB C-terminal domain.

Last update:

January 2023 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

TONB_CTD, PS52015; TonB C-terminal domain profile  (MATRIX)


1AuthorsOeemig J.S. Ollila O.H.S. Iwai H.
TitleNMR structure of the C-terminal domain of TonB protein from Pseudomonas aeruginosa.
SourcePeerJ 6:E5412-E5412(2018).
PubMed ID30186676

2AuthorsKoedding J. Killig F. Polzer P. Howard S.P. Diederichs K. Welte W.
TitleCrystal structure of a 92-residue C-terminal fragment of TonB from Escherichia coli reveals significant conformational changes compared to structures of smaller TonB fragments.
SourceJ. Biol. Chem. 280:3022-3028(2005).
PubMed ID15522863

3AuthorsPeacock R.S. Weljie A.M. Howard S.P. Price F.D. Vogel H.J.
TitleThe solution structure of the C-terminal domain of TonB and interaction studies with TonB box peptides.
SourceJ. Mol. Biol. 345:1185-1197(2005).
PubMed ID15644214

4Authorsde Amorim G.C. Prochnicka-Chalufour A. Delepelaire P. Lefevre J. Simenel C. Wandersman C. Delepierre M. Izadi-Pruneyre N.
TitleThe structure of HasB reveals a new class of TonB protein fold.
SourcePLoS One. 8:E58964-E58964(2013).
PubMed ID23527057

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