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The TolQ Membrane-spanning domains
The TolQ Membrane-spanning domains [1]


TolQ is a polytopic protein located in the inner (cytoplasmic) membrane, containing approximately 230 amino acids. There are three membrane spanning segments in TolQ with each segment containing an α-helix[2]. TM1 is connected to TM2 via a large cytoplasmic loop, with the N-terminal ending in the periplasm. This topology is also found in ExbB, which can be explained by the similar sequence shared by both proteins[3].

It has been shown that 4 to 6 TolQ molecules associate in the TolQRA complex, and that they form multimers which interact with the transmembrane helices (TMH) of TolQ, TolR and TolA[4]. The multimers are formed by the three TMHs of TolQ, the last of which undergo a conformational change to form a hairpin, while the first TMH forms an intermolecular interaction[5].


TolQ plays an important role in the maintenance of the bacterial envelope integrity as well as the import of filamentous bacteriophage and group A colicins[5].

Loss of TolQ function can be partially replaced by ExbB and vice versa - reduced activities of either of these proteins via a mutant form can be reversed by introducing double mutants[3].


  1. Lewin TM, Webster RE. Membrane insertion characteristics of the various transmembrane domains of the Escherichia coli TolQ protein. J Biol Chem. 1996 Jun 14;271(24):14143-9. PMID:8662905
  2. Lazzaroni JC, Vianney A, Popot JL, Benedetti H, Samatey F, Lazdunski C, Portalier R, Geli V. Transmembrane alpha-helix interactions are required for the functional assembly of the Escherichia coli Tol complex. J Mol Biol. 1995 Feb 10;246(1):1-7. PMID:7853390 doi:
  3. 3.0 3.1 Braun V, Herrmann C. Point mutations in transmembrane helices 2 and 3 of ExbB and TolQ affect their activities in Escherichia coli K-12. J Bacteriol. 2004 Jul;186(13):4402-6. PMID:15205446 doi:10.1128/JB.186.13.4402-4406.2004
  4. Zhang XY, Goemaere EL, Seddiki N, Celia H, Gavioli M, Cascales E, Lloubes R. Mapping the interaction between Escherichia coli TolQ transmembrane segments. J Biol Chem. 2011 Feb 1. PMID:21285349 doi:10.1074/jbc.M110.192773
  5. 5.0 5.1 Vianney A, Lewin TM, Beyer WF Jr, Lazzaroni JC, Portalier R, Webster RE. Membrane topology and mutational analysis of the TolQ protein of Escherichia coli required for the uptake of macromolecules and cell envelope integrity. J Bacteriol. 1994 Feb;176(3):822-9. PMID:8300535

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