InterPro domain: IPR011531

Bicarbonate (HCO ₃ ^- ) transport mechanisms are the principal regulators of pH in animal cells. Such transport also plays a vital role in acid-base movements in the stomach, pancreas, intestine, kidney, reproductive organs and the central nervous system. Functional studies have suggested four different HCO ₃ ^- transport modes. Anion exchanger proteins exchange HCO ₃ ^- for Cl ^- in a reversible, electroneutral manner [ 1 ]. Na ⁺ /HCO ₃ ^- co-transport proteins mediate the coupled movement of Na ⁺ and HCO ₃ ^- across plasma membranes, often in an electrogenic manner [ 2 ]. Na ^- driven Cl ^- /HCO ₃ ^- exchange and K ⁺ /HCO ₃ ^- exchange activities have also been detected in certain cell types, although the molecular identities of the proteins responsible remain to be determined.

Sequence analysis of the two families of HCO ₃ ^- transporters that have been cloned to date (the anion exchangers and Na ⁺ /HCO ₃ ^- co-transporters) reveals that they are homologous. This is not entirely unexpected, given that they both transport HCO ₃ ^- and are inhibited by a class of pharmacological agents called disulphonic stilbenes [ 3 ]. They share around ~25-30% sequence identity, which is distributed along their entire sequence length, and have similar predicted membrane topologies, suggesting they have ~10 transmembrane (TM) domains.

This domain is found at the C terminus of many bicarbonate transport proteins. It is also found in some plant proteins responsible for boron transport [ 4 ]. In these proteins it covers almost the entire length of the sequence.

1. Molecular biology of the anion exchanger gene family. Int. Rev. Cytol. 123, 177-99
2. The electrogenic Na/HCO3 cotransporter. Wien. Klin. Wochenschr. 109, 445-56
3. Cloning and functional expression of a human kidney Na+:HCO3- cotransporter. J. Biol. Chem. 272, 19111-4
4. Arabidopsis boron transporter for xylem loading. Nature 420, 337-40