A conductive pathway generated from fragments of the human red cell anion exchanger AE1

Mark D. Parker, Mark T. Young, Christopher M. Daly, Robert W. Meech, Walter F. Boron, Michael J. A. Tanner (2007) Department of 1Biochemistry and 2Physiology, University of Bristol,The Journal of Physiology 581 (1), 33–50. doi:10.1113/jphysiol.2007.128389
Human red cell anion exchanger AE1 (band 3) is an electroneutral Cl–HCO3 exchanger with 12–14 transmembrane spans (TMs). Previous work using Xenopus oocytes has shown that two co-expressed fragments of AE1 lacking TMs 6 and 7 are capable of forming a stilbene disulphonate-sensitive 36Cl-influx pathway, reminiscent of intact AE1. In the present study, they create a single construct, AE1Δ(6: 7), representing the intact protein lacking TMs 6 and 7. They expressed this construct in Xenopus oocytes and evaluated it employing a combination of two-electrode voltage clamp and pH-sensitive microelectrodes. They found that, whereas AE1Δ(6: 7) has some electroneutral Cl–base exchange activity, the protein also forms a novel anion-conductive pathway that is blocked by DIDS. The mutation Lys539Ala at the covalent DIDS-reaction site of AE1 reduced the DIDS sensitivity, demonstrating that (1) the conductive pathway is intrinsic to AE1Δ(6: 7) and (2) the conductive pathway has some commonality with the electroneutral anion-exchange pathway. The conductance has an anion-permeability sequence: NO3 ≈ I > NO2 > Br > Cl > SO42 ≈ HCO3 ≈ gluconate ≈ aspartate ≈ cyclamate . It may also have a limited permeability to Na+ and the zwitterion taurine. Although this conductive pathway is not a usual feature of intact mammalian AE1, it shares many properties with the anion-conductive pathways intrinsic to two other Cl–HCO3 exchangers, trout AE1 and mammalian SLC26A7.