title: X-ray structure of EmrE supports dual topology model.
abstract: EmrE, a multidrug transporter from Escherichia coli, functions as a homodimer of a small four-transmembrane protein. The membrane insertion topology of the two monomers is controversial. Although the EmrE protein was reported to have a unique orientation in the membrane, models based on electron microscopy and now defunct x-ray structures, as well as recent biochemical studies, posit an antiparallel dimer. We have now reanalyzed our x-ray data on EmrE. The corrected structures in complex with a transport substrate are highly similar to the electron microscopy structure. The first three transmembrane helices from each monomer surround the substrate binding chamber, whereas the fourth helices participate only in dimer formation. Selenomethionine markers clearly indicate an antiparallel orientation for the monomers, supporting a "dual topology" model.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, CB-105, La Jolla, CA 92037, USA.
authors.forename: Yen-Ju
authors.initials: YJ
authors.lastname: Chen
authors.forename: Owen
authors.initials: O
authors.lastname: Pornillos
authors.forename: Samantha
authors.initials: S
authors.lastname: Lieu
authors.forename: Che
authors.initials: C
authors.lastname: Ma
authors.forename: Andy P
authors.initials: AP
authors.lastname: Chen
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry*; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry*; D005454:Fluorescence Polarization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D012645:Selenomethionine / Q000032:analysis
chemical_list: D017920:Antiporters; D029968:Escherichia coli Proteins; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D011994:Recombinant Proteins; C075436:EmrE protein, E coli; D012645:Selenomethionine; C013289:tetraphenylphosphonium