[1] Members of the AE family are generally responsible for the transport of anions across cellular barriers, although their functions may vary.
Characterized protein members of the AE family are found in plants, animals, insects and yeast.
Uncharacterized AE homologues may be present in bacteria (e.g., in Enterococcus faecium, 372 aas; gi 22992757; 29% identity in 90 residues).
Their N-terminal hydrophilic domains may interact with cytoskeletal proteins and therefore play a cell structural role.
Such transport also plays a vital role in acid-base movements in the stomach, pancreas, intestine, kidney, reproductive organs and the central nervous system.
Sequence analysis of the two families of HCO3 − transporters that have been cloned to date (the anion exchangers and Na+/HCO3 − co-transporters) reveals that they are homologous.
This is not entirely unexpected, given that they both transport HCO3 − and are inhibited by a class of pharmacological agents called disulphonic stilbenes.
SLC4 proteins play roles in acid-base homeostasis, transport of H+ or HCO−3 by epithelia (e.g. absorption of HCO−3 in the renal proximal tubule, secretion of HCO−3 in the pancreatic duct), as well as the regulation of cell volume and intracellular pH.
[8] Based on their hydropathy plots all SLC4 proteins are hypothesized to share a similar topology in the cell membrane.
Although the C-terminal domain comprises a small percentage of the size of the protein, this domain in some cases, has (i) binding motifs that may be important for protein-protein interactions (e.g., AE1, AE2, and NBCn1), (ii) is important for trafficking to the cell membrane (e.g., AE1 and NBCe1), and (iii) may provide sites for regulation of transporter function via protein kinase A phosphorylation (e.g., NBCe1).
[13] AE1 in human red blood cells has been shown to transport a variety of inorganic and organic anions.
The rate of flipping is sufficiently rapid to suggest that this AE1-catalyzed process is physiologically important in red blood cells and possibly in other animal tissues as well.
They catalyze the reabsorption of HCO−3 in the renal proximal tubule in an electrogenic process that is inhibited by typical stilbene inhibitors of AE such as DIDS and SITS.
Animal cells in tissue culture expressing the gene-encoding the ABC-type chloride channel protein CFTR (TC# 3.A.1.202.1) in the plasma membrane have been reported to exhibit cyclic AMP-dependent stimulation of AE activity.
[5] In A. thaliana, boron is exported from pericycle cells into the root stellar apoplasm against a concentration gradient for uptake into the shoots.