Band 3
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| 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 | P02730 |
| Other data | |
| Locus | Chr. 2 p23.3 |
Band 3 anion transport protein also known as anion exchanger 1 (AE1) or band 3 or solute carrier family 4 member 1 (SLC4A1) is a protein that in humans is encoded by the SLC4A1 gene.
Band 3 anion transport protein 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]
Contents
Function
This is present in the α-intercalated cells of the collecting ducts of the nephron. these are the main acid secreting cells of the kidney. They generate 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. Here it performs two functions:
- Electroneutral chloride and bicarbonate exchange across the plasma membrane on a one-for-one basis.This is crucial for CO2 uptake by the red blood cell and conversion (by hydration catalysed by carbonic anhydrase) into a proton and a bicarbonate ion. The bicarbonate is then extruded (in exchange for a chloride) from the cell by the band 3 molecule.
- Physical linkage of the plasma membrane to the underlying membrane skeleton (via binding with ankyrin and protein 4.2). This appears to be to prevent membrane surface loss, rather than being to do with membrane skeleton assembly.
Distribution
It is ubiquitous throughout the vertebrates. In mammals it is present in two specific sites:
- the erythrocyte (red blood cell) cell membrane and
- the basolateral surface of the alpha-intercalated cell (the acid secreting cell type) in the collecting duct of the kidney.
Gene products
The erythrocyte and kidney forms are different isoforms of the same protein.[2]
The erythrocyte form of AE1 (eAE1) is composed of 911 amino acids. eAE1 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 eAE1.
A different isoform of AE1, known as kAE1 (which is 65 amino acids shorter than erythroid AE1) is found in the basolateral membrane of alpha-intercalated cells in the cortical collecting duct of the kidney.
Clinical significance
Mutations of kidney AE1 cause distal (type1) renal tubular acidosis, which is an inability to acidify the urine, even if the blood is too acidic. 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.
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 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]
Interactions
Band 3 has been shown to interact with CA2[5][6][7][8] and CA4.[9]
Discovery
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'.
See also
References
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Further reading
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External links
- Diego blood group system at BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH
- Band 3 Protein at the US National Library of Medicine Medical Subject Headings (MeSH)
- Chloride-Bicarbonate Antiporters at the US National Library of Medicine Medical Subject Headings (MeSH)
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