title: The functional and physical relationship between the DRA bicarbonate transporter and carbonic anhydrase II.
abstract: COOH-terminal cytoplasmic tails of chloride/bicarbonate anion exchangers (AE) bind cytosolic carbonic anhydrase II (CAII) to form a bicarbonate transport metabolon, a membrane protein complex that accelerates transmembrane bicarbonate flux. To determine whether interaction with CAII affects the downregulated in adenoma (DRA) chloride/bicarbonate exchanger, anion exchange activity of DRA-transfected HEK-293 cells was monitored by following changes in intracellular pH associated with bicarbonate transport. DRA-mediated bicarbonate transport activity of 18 +/- 1 mM H+ equivalents/min was inhibited 53 +/- 2% by 100 mM of the CAII inhibitor, acetazolamide, but was unaffected by the membrane-impermeant carbonic anhydrase inhibitor, 1-[5-sulfamoyl-1,3,4-thiadiazol-2-yl-(aminosulfonyl-4-phenyl)]-2,6-dimethyl-4-phenyl-pyridinium perchlorate. Compared with AE1, the COOH-terminal tail of DRA interacted weakly with CAII. Overexpression of a functionally inactive CAII mutant, V143Y, reduced AE1 transport activity by 61 +/- 4% without effect on DRA transport activity (105 +/- 7% transport activity relative to DRA alone). We conclude that cytosolic CAII is required for full DRA-mediated bicarbonate transport. However, DRA differs from other bicarbonate transport proteins because its transport activity is not stimulated by direct interaction with CAII.
authors.affiliation: Canadian Institutes of Health Research Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Deborah
authors.initials: D
authors.lastname: Sterling
authors.forename: Nathan J D
authors.initials: NJ
authors.lastname: Brown
authors.forename: Claudiu T
authors.initials: CT
authors.lastname: Supuran
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Casey
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000236:Adenoma / Q000378:metabolism; D017920:Antiporters; D001639:Bicarbonates / Q000378:metabolism*; D024402:Carbonic Anhydrase II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D000076988:Sulfate Transporters; D014162:Transfection
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D008565:Membrane Proteins; C081011:SLC26A3 protein, human; D000076988:Sulfate Transporters; D024402:Carbonic Anhydrase II; D000086:Acetazolamide