Entry to "formula tunnel" revealed by SLC4A4 human mutation and structural model.

Abstract

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 HCO(3)(-) permeation.

• Authors: Min-Hwang Chang, Jennifer DiPiero, Frank D Sönnichsen, Michael F Romero
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 283 Issue 26 Pg. 18402-10 (Jun 27 2008) ISSN: 0021-9258 [Print] United States
• PMID: 18441326 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• SLC4A4 protein, human
• Sodium-Bicarbonate Symporters
• Solvents

Topics

• Amino Acid Sequence
• Animals
• Humans
• Hydrogen-Ion Concentration
• Molecular Sequence Data
• Mutagenesis, Site-Directed
• Mutation
• Oocytes (metabolism)
• Point Mutation
• Protein Conformation
• Protein Structure, Tertiary
• Sequence Homology, Amino Acid
• Sodium-Bicarbonate Symporters (chemistry, genetics)
• Solvents (chemistry)
• Xenopus