solute carrier family 4 (anion exchanger), member 1, adapter protein | |
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Identifiers | |
Symbol | SLC4A1AP |
Entrez | 22950 |
HUGO | 13813 |
OMIM | 602655 |
RefSeq | NM_018158 |
UniProt | Q9BWU0 |
Other data | |
Locus | Chr. 2 p23.3 |
Anion Exchanger 1 (AE1) or Band 3 is a phylogenetically preserved transport protein responsible for mediating the exchange of chloride (Cl-) for bicarbonate (HCO3-) across a plasma membrane. Functionally similar members of the AE clade are AE2 and AE3.[1]
It is ubiquitous throughout the vertebrates. In humans it is present in two specific sites:
The erythrocyte and kidney forms are different isoforms of the same protein.
Contents |
AE1 was discovered following SDS-PAGE gel electrophoresis of erythrocyte cell membrane. The large 'third' band on the electrophoresis gel represented AE1, which was thus initially termed 'Band 3'. The chloride-bicarbonate exchanger in the red cell membrane is not a pump, which would use metabolic energy. Nor is it strictly an enzyme. It is protein counter-transporter, known as band III.[2]
AE1 is an important structural component of the erythrocyte cell membrane, making up to 25% of the cell membrane surface. Each red cell contains approximately one million copies of AE1.
Here it performs two functions:
Mutations of erythroid AE1 affecting the extracellular domains of the molecule may cause alterations in the individual's blood group, as band 3 determines the Diego blood group.
More importantly erythroid AE1 mutations cause between 15-25% of cases of Hereditary spherocytosis (a disorder associated with progressive red cell membrane loss), and also cause the hereditary conditions of Hereditary stomatocytosis [3] and Southeast Asian Ovalocytosis [4]
A different isoform of AE1, known as kAE1 (which is 65 amino acids shorter than erythroid AE1) is found in the basolateral surface of the alpha-intercalated cell in the cortical collecting duct of the kidney.
This is the principal acid secreting cell of the kidney, which generates hydrogen ions and bicarbonate ions from carbon dioxide and water-a reaction catalysed by Carbonic anhydrase.
The hydrogen ions are pumped into the collecting duct tubule by vacuolar H+ATPase, the apical proton pump,which thus excretes acid into the urine.
kAE1 exchanges bicarbonate for chloride on the basolateral surface, essentially returning bicarbonate to the blood.
Mutations of kidney AE1 cause distal (type1) renal tubular acidosis, which is an inability to acidify the urine, even if the blood is too acid. These mutations are disease causing as they cause mistargetting of the mutant band 3 proteins so that they are retained within the cell or occasionally addressed to the wrong (i.e. apical) surface.
Band 3 has been shown to interact with Carbonic anhydrase II[5][6][7][8] and CA4.[9]
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