title: Identification of oligomerization and drug-binding domains of the membrane fusion protein EmrA.
abstract: Many pathogenic Gram-negative bacteria possess tripartite transporters that catalyze drug extrusion across the inner and outer membranes, thereby conferring resistance. These transporters consist of inner (IMP) and outer (OMP) membrane proteins, which are coupled by a periplasmic membrane fusion (MFP) protein. However, it is not know whether the MFP translocates the drug between the membranes, by acting as a channel, or whether it brings the IMP and OMP together, facilitating drug transfer. The MFP EmrA has an elongated periplasmic domain, which binds transported drugs, and is anchored to the inner membrane by a single alpha-helix, which contains a leucine zipper dimerization domain. Consistent with CD and hydrodynamic analyses, the periplasmic domain is predicted to be composed of a beta-sheet subdomain and an alpha-helical coiled-coil. We propose that EmrA forms a trimer in which the coiled-coils radiate across the periplasm, where they could sequester the OMP TolC. The "free" leucine zipper in the EmrA trimer might stabilize the interaction with the IMP EmrB, which also possesses leucine zipper motifs in the putative N- and C-terminal helices. The beta-sheet subdomain of EmrA would sit at the membrane surface adjacent to the EmrB, from which it receives the transported drug, inducing a conformational change that triggers the interaction with the OMP.
authors.affiliation: Centre for Infectious Diseases, Wolfson Research Institute, University of Durham, Queen's Campus, Stockton-on-Tees, TS17 6BH, United Kingdom.
authors.forename: M Ines
authors.initials: MI
authors.lastname: Borges-Walmsley
authors.forename: Jeremy
authors.initials: J
authors.lastname: Beauchamp
authors.forename: Sharon M
authors.initials: SM
authors.lastname: Kelly
authors.forename: Kornelia
authors.initials: K
authors.lastname: Jumel
authors.forename: Denise
authors.initials: D
authors.lastname: Candlish
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Harding
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Price
authors.forename: Adrian R
authors.initials: AR
authors.lastname: Walmsley
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D003001:Cloning, Molecular; D017931:DNA Primers; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D006193:Haemophilus influenzae / Q000378:metabolism; D016623:Ion Pumps / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D016133:Polymerase Chain Reaction; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; C489681:EmrA protein, E coli; D029968:Escherichia coli Proteins; D016623:Ion Pumps; D046911:Macromolecular Substances; D008565:Membrane Proteins; C077168:emrA protein, Bacteria; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone