Consequences of point mutations in trout anion exchanger 1 (tAE1) transmembrane domains: evidence that tAE1 can behave as a chloride channel.
In this study, we have shown that, when expressed in Xenopus oocytes, trout anion exchanger 1 (tAE1) was able to act as a bifunctional protein, either an anion exchanger or a chloride conductance. Point mutations of tAE1 were carried out and their effect on Cl- conductance and Cl- unidirectional flux were studied. We have shown that mutations made in transmembrane domain 7 had dramatic effects on tAE1 function. Indeed, when these residues were mutated, either individually or together (mutants E632K, D633G, and ED/KG), Cl- conductance was reduced to 28-44% that of wild-type tAE1. Moreover, ion substitution experiments showed that anion selectivity was altered. However, the exchanger function was unchanged, as evidenced by the fact that Cl- influx and K(m) were identical for each of these mutants and similar to the wild-type protein parameters. By contrast, mutations made in the C-terminal domains of the protein (R819M, Q829K) affected both transport functions. Cl- conductance was increased by approximately 200% with respect to tAE1 and anion selectivity was impaired. Likewise, Cl- influx was increased by approximately 260% and was no longer saturable. These and other mutations carried out in transmembrane domains 7, 8, 12-14 of tAE1 allow us to demonstrate without doubt that, in addition to its anion exchanger activity, tAE1 can also function as a chloride channel. Above all, this work led us to identify amino acids involved in this double function organization.
Martial
Sonia
S
Laboratoire de Physiologie des Membranes Cellulaires, FRE 2721, CNRS-Université de Nice, Bâtiment de Sciences Naturelles, Parc Valrose, 28 av Valrose Nice Cedex 2, France.
Guizouarn
Hélène
H
Gabillat
Nicole
N
Pellissier
Bernard
B
Borgese
Franck
F
D000595:Amino Acid Sequence; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics* / Q000378:metabolism*; D018118:Chloride Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002713:Chlorine / Q000737:chemistry / Q000378:metabolism; D004594:Electrophysiology; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000235:genetics; D016415:Sequence Alignment; D014337:Trout / Q000235:genetics* / Q000378:metabolism*; D014982:Xenopus laevis
D001457:Anion Exchange Protein 1, Erythrocyte; D018118:Chloride Channels; D002713:Chlorine