title: Mapping the interactions between Escherichia coli TolQ transmembrane segments.
abstract: The tolQRAB-pal operon is conserved in Gram-negative genomes. The TolQRA proteins of Escherichia coli form an inner membrane complex in which TolQR uses the proton-motive force to regulate TolA conformation and the in vivo interaction of TolA C-terminal region with the outer membrane Pal lipoprotein. The stoichiometry of the TolQ, TolR, and TolA has been estimated and suggests that 4-6 TolQ molecules are associated in the complex, thus involving interactions between the transmembrane helices (TMHs) of TolQ, TolR, and TolA. It has been proposed that an ion channel forms at the interface between two TolQ and one TolR TMHs involving the TolR-Asp(23), TolQ-Thr(145), and TolQ-Thr(178) residues. To define the organization of the three TMHs of TolQ, we constructed epitope-tagged versions of TolQ. Immunodetection of in vivo and in vitro chemically cross-linked TolQ proteins showed that TolQ exists as multimers in the complex. To understand how TolQ multimerizes, we initiated a cysteine-scanning study. Results of single and tandem cysteine substitution suggest a dynamic model of helix interactions in which the hairpin formed by the two last TMHs of TolQ change conformation, whereas the first TMH of TolQ forms intramolecular interactions.
authors.affiliation: Laboratoire d'Ingénierie des Systèmes Macromoleculaires UPR9027, CNRS, Aix-Marseille Université, Marseille, France.
authors.forename: Xiang Y-Z
authors.initials: XY
authors.lastname: Zhang
authors.forename: Emilie L
authors.initials: EL
authors.lastname: Goemaere
authors.forename: Nadir
authors.initials: N
authors.lastname: Seddiki
authors.forename: Hervé
authors.initials: H
authors.lastname: Célia
authors.forename: Marthe
authors.initials: M
authors.lastname: Gavioli
authors.forename: Eric
authors.initials: E
authors.lastname: Cascales
authors.forename: Roland
authors.initials: R
authors.lastname: Lloubes
mesh_terms: D019943:Amino Acid Substitution; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D010449:Peptide Mapping / Q000379:methods; D017434:Protein Structure, Tertiary
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D046912:Multiprotein Complexes; C062093:tolA protein, E coli; C060792:tolQ protein, E coli; C060794:tolR protein, E coli