Entry to "HCO3- tunnel" revealed by SLC4A4 human mutation and structural model

Min Hwang Chang, Jennifer DiPiero, Frank D. Sönnichsen, Michael F. Romero

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


Glaucoma, cataracts, and proximal renal tubular acidosis are diseases caused by point mutations in the human electrogenic Na+ bicarbonate cotransporter (NBCe1/SLC4A4) (1, 2). One such mutation, R298S, is located in the cytoplasmic N-terminal domain of NBCe1 and has only moderate (75%) function. As SLC transporters have high similarity in their membrane and N-terminal primary sequences, we homology-modeled NBCe1 onto the crystal structure coordinates of Band 3(AE1) (3). Arg-298 is predicted to be located in a solvent-inaccessible subsurface pocket and to associate with Glu-91 or Glu-295 via H-bonding and charge-charge interactions. We perturbed these putative interactions between Glu-91 and Arg-298 by site-directed mutagenesis and used expression in Xenopus oocyte to test our structural model. Mutagenesis of either residue resulted in reduced transport function. Function was "repaired" by charge reversal (E91R/R298E), implying that these two residues are interchangeable and interdependent. These results contrast the current understanding of the AE1 N terminus as protein-binding sites and propose that hkNBCe1 (and other SLC4) cytoplasmic N termini play roles in controlling HCO3- permeation.

Original languageEnglish (US)
Pages (from-to)18402-18410
Number of pages9
JournalJournal of Biological Chemistry
Issue number26
StatePublished - Jun 27 2008

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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