title: Projection structure of a member of the amino acid/polyamine/organocation transporter superfamily.
abstract: The L-arginine/agmatine antiporter AdiC is a key component of the arginine-dependent extreme acid resistance system of Escherichia coli. Phylogenetic analysis indicated that AdiC belongs to the amino acid/polyamine/organocation (APC) transporter superfamily having sequence identities of 15-17% to eukaryotic and human APC transporters. For functional and structural characterization, we cloned, overexpressed, and purified wild-type AdiC and the point mutant AdiC-W293L, which is unable to bind and consequently transport L-arginine. Purified detergent-solubilized AdiC particles were dimeric. Reconstitution experiments yielded two-dimensional crystals of AdiC-W293L diffracting beyond 6 angstroms resolution from which we determined the projection structure at 6.5 angstroms resolution. The projection map showed 10-12 density peaks per monomer and suggested mainly tilted helices with the exception of one distinct perpendicular membrane spanning alpha-helix. Comparison of AdiC-W293L with the projection map of the oxalate/formate antiporter from Oxalobacter formigenes, a member from the major facilitator superfamily, indicated different structures. Thus, two-dimensional crystals of AdiC-W293L yielded the first detailed view of a transport protein from the APC superfamily at sub-nanometer resolution.
authors.affiliation: M. E. Müller Institute for Structural Biology, Biozentrum of the University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Casagrande
authors.forename: Merce
authors.initials: M
authors.lastname: Ratera
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Schenk
authors.forename: Mohamed
authors.initials: M
authors.lastname: Chami
authors.forename: Eva
authors.initials: E
authors.lastname: Valencia
authors.forename: Jesus Maria
authors.initials: JM
authors.lastname: Lopez
authors.forename: David
authors.initials: D
authors.lastname: Torrents
authors.forename: Andreas
authors.initials: A
authors.lastname: Engel
authors.forename: Manuel
authors.initials: M
authors.lastname: Palacin
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Fotiadis
mesh_terms: D026905:Amino Acid Transport Systems / Q000737:chemistry* / Q000235:genetics; D026923:Amino Acid Transport Systems, Basic / Q000737:chemistry* / Q000235:genetics; D000818:Animals; D017920:Antiporters / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D020624:Oxalobacter formigenes / Q000737:chemistry / Q000235:genetics; D010802:Phylogeny; D020836:Protein Structure, Quaternary / Q000502:physiology
chemical_list: C476528:AdiC protein, E coli; D026905:Amino Acid Transport Systems; D026923:Amino Acid Transport Systems, Basic; D017920:Antiporters; D029968:Escherichia coli Proteins