Band 3 anion transport protein

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 is encoded by the SLC4A1 gene in humans.

Band 3 anion transport protein is a

Band 3 is present in the basolateral face of the α-intercalated cells of the collecting ducts of the nephron, which 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:^{[citation needed]}

• 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 excreted (in exchange for a chloride) from the cell by band 3.
• 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 having to do with membrane skeleton assembly.

Distribution

It is ubiquitous throughout the

• the
  erythrocyte
  (red blood cell) cell membrane and
• the
  collecting duct of the kidney
  .

The erythrocyte isoform of AE1, known as 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.^[citation needed]

The kidney isoform of AE1, known as kAE1 (which is 65 amino acids shorter than erythroid AE1) is found in the

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 antigen system (blood group).^{[citation needed]}

More importantly erythroid AE1 mutations cause 15–25% of cases of

AE1 was discovered following SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) of erythrocyte cell membrane. The large 'third' band on the electrophoresis gel represented AE1, which was thus initially termed 'Band 3'.^[14]

See also

• Cluster of differentiation
• Anion exchanger family

References