title: Structures of intermediate transport states of ZneA, a Zn(II)/proton antiporter.
abstract: Efflux pumps belonging to the ubiquitous resistance-nodulation-cell division (RND) superfamily transport substrates out of cells by coupling proton conduction across the membrane to a conformationally driven pumping cycle. The heavy metal-resistant bacteria Cupriavidus metallidurans CH34 relies notably on as many as 12 heavy metal efflux pumps of the RND superfamily. Here we show that C. metallidurans CH34 ZneA is a proton driven efflux pump specific for Zn(II), and that transport of substrates through the transmembrane domain may be electrogenic. We report two X-ray crystal structures of ZneA in intermediate transport conformations, at 3.0 and 3.7 Å resolution. The trimeric ZneA structures capture protomer conformations that differ in the spatial arrangement and Zn(II) occupancies at a proximal and a distal substrate binding site. Structural comparison shows that transport of substrates through a tunnel that links the two binding sites, toward an exit portal, is mediated by the conformation of a short 14-aa loop. Taken together, the ZneA structures presented here provide mechanistic insights into the conformational changes required for substrate efflux by RND superfamily transporters.
authors.affiliation: Department of Biochemistry and Biophysics, Center for the Structure of Membrane Proteins, Membrane Protein Expression Center, University of California, San Francisco, CA 94158.
authors.forename: John Edward
authors.initials: JE
authors.lastname: Pak
authors.forename: Elisabeth Ngonlong
authors.initials: EN
authors.lastname: Ekendé
authors.forename: Efrem G
authors.initials: EG
authors.lastname: Kifle
authors.forename: Joseph Daniel
authors.initials: JD
authors.lastname: O'Connell
authors.forename: Fabien
authors.initials: F
authors.lastname: De Angelis
authors.forename: Meseret B
authors.initials: MB
authors.lastname: Tessema
authors.forename: Kheiro-Mouna
authors.initials: KM
authors.lastname: Derfoufi
authors.forename: Yaneth
authors.initials: Y
authors.lastname: Robles-Colmenares
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Robbins
authors.forename: Erik
authors.initials: E
authors.lastname: Goormaghtigh
authors.forename: Guy
authors.initials: G
authors.lastname: Vandenbussche
authors.forename: Robert M
authors.initials: RM
authors.lastname: Stroud
mesh_terms: D017920:Antiporters / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D001692:Biological Transport / Q000235:genetics; D003460:Crystallization; D049921:Cupriavidus / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D011522:Protons; D014961:X-Ray Diffraction; D015032:Zinc / Q000378:metabolism*
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D011522:Protons; D015032:Zinc