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Band 3

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Title: Band 3  
Author: World Heritage Encyclopedia
Language: English
Subject: Solute carrier family, Red blood cell, SLC44A1, RHAG, SLC2A13
Collection: Blood Antigen Systems, Blood Proteins, Clusters of Differentiation, Enzymes, Solute Carrier Family, Transfusion Medicine
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Band 3

solute carrier family 4 (anion exchanger), member 1, adapter protein
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 1
  • Distribution 2
  • Gene products 3
  • Clinical significance 4
  • Interactions 5
  • Discovery 6
  • See also 7
  • References 8
  • Further reading 9
  • External links 10

Function

This is present in 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. 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:

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

  1. ^
  2. ^
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^
  8. ^
  9. ^

Further reading

External links


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