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The Glutamate Substitution of Aspartate555 of the Electrogenic Sodium/Bicarbonate Cotransporter NBCe1 Alters Bicarbonate Selectivity
Author(s) -
Choi Inyeong
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1283-b
Subject(s) - chemistry , cotransporter , intracellular ph , bicarbonate , reversal potential , biophysics , sodium , membrane potential , intracellular , nigericin , conductance , symporter , sodium bicarbonate , biochemistry , transporter , membrane , patch clamp , biology , gene , organic chemistry , receptor , mathematics , combinatorics
To examine the structural requirements for electrogenicity of the sodium/bicarbonate cotransporter NBCe1, we mutated amino acid resides, in transmembrane domains, that are least conserved between electrogenic Na/HCO 3 transporters and electroneutral Na/HCO 3 transporters. Among these mutants, D555E (substitution of Asp 555 with a Glu) had a significant decrease in HCO 3 − conductance. Immunocytochemistry showed a strong fluorescence labeling in plasma membranes of oocytes expressing D555E. In 5% CO 2 /26 mM HCO 3 − , oocytes expressing D555E recovered intracellular pH from an acidification and produced an outward current comparable to ~25% of the current in oocytes expressing wild type NBCe1. Na + removal in the continued presence of CO 2 /HCO 3 − reversed intracellular pH recovery and reduced the current. However, the current upon Na + or HCO 3 − removal was no less than the initial current produced in CO 2 /HCO 3 − ‐free solution. The D555E‐mediated conductance was significantly reduced by Cl − removal, indicating that D555E can transport Cl − . Anion substitution showed that oocytes expressing D555E had relatively weak HCO 3 − selectivity, producing currents with other monovalent anions. Substituting Asp 555 with an Asn affected in the reversal potential of the HCO 3 − currents with negligible change in the conductance. We conclude that Asp 555 is involved in anion selectivity of NBCe1.