title: Three-dimensional model for the human Cl-/HCO3- exchanger, AE1, by homology to the E. coli ClC protein.
abstract: AE1 mediates electroneutral 1:1 exchange of bicarbonate for chloride across the plasma membrane of erythrocytes and type A cells of the renal collecting duct. No high-resolution structure is available for the AE1 membrane domain, which alone is required for its transport activity. A recent electron microscopy structure of the AE1 membrane domain was proposed to have a similar protein fold to ClC chloride channels. We developed a three-dimensional homology model of the AE1 membrane domain, using the Escherichia coli ClC channel structure as a template. This model agrees well with a long list of biochemically established spatial constraints for AE1. To investigate the AE1 transport mechanism, we created point mutations in regions corresponding to E. coli ClC transport mechanism residues. When expressed in HEK293 cells, several mutants had Cl(-)/HCO3(-) exchange rates significantly different from that of wild-type AE1. When further assessed in Xenopus laevis oocytes, there were significant changes in the transport activity of several AE1 point mutants as assessed by changes in pH. None of the mutants, however, added an electrogenic component to AE1 transport activity. This indicates that the AE1 point mutants altered the transport activity of AE1, without changing its electrogenicity and stoichiometry. The homology model successfully identified residues in AE1 that are critical to AE1 transport activity. Thus, we conclude that AE1 has a similar protein fold to ClC chloride channels.
authors.affiliation: Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, Canada T6G 2H7.
authors.forename: Pamela
authors.initials: P
authors.lastname: Bonar
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Schneider
authors.forename: Holger M
authors.initials: HM
authors.lastname: Becker
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Deitmer
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Casey
mesh_terms: D000595:Amino Acid Sequence; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000737:chemistry; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D018118:Chloride Channels; C508370:ClC protein, E coli; D029968:Escherichia coli Proteins; D050505:Mutant Proteins