Band 3

Solute carrier family 4, anion exchanger, member 1 (erythrocyte membrane protein band 3, Diego blood group)
Atomic microscope image of Band 3
Available structures PDB 1BH7, 1BNX, 1BTQ, 1BTR, 1BTS, 1BTT, 1BZK, 1HYN, 2BTA, 2BTB, 3BTB
Identifiers
Symbols	SLC4A1; AE1; BND3; CD233; DI; EMPB3; EPB3; FR; MGC116750; MGC116753; MGC126619; MGC126623; RTA1A; SW; WD; WD1; WR
External IDs	OMIM: 109270 MGI: 109393 HomoloGene: 37290 GeneCards: SLC4A1 Gene
Gene Ontology Molecular function • actin binding • transporter activity • inorganic anion exchanger activity • protein binding • protein C-terminus binding • anion transmembrane transporter activity • chloride transmembrane transporter activity • anion:anion antiporter activity • ankyrin binding • protein homodimerization activity • protein anchor Cellular component • plasma membrane • integral to plasma membrane • integral to membrane • basolateral plasma membrane • Z disc • cortical cytoskeleton Biological process • ion transport • anion transport • chloride transport • cellular ion homeostasis • bicarbonate transport • transmembrane transport Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	6521	20533
Ensembl	ENSG00000004939	ENSMUSG00000006574
UniProt	P02730	Q3TA19
RefSeq (mRNA)	NM_000342.3	NM_011403.2
RefSeq (protein)	NP_000333.1	NP_035533.1
Location (UCSC)	Chr 17: 42.33 – 42.35 Mb	Chr 11: 102.21 – 102.23 Mb
PubMed search	[1]	[2]

solute carrier family 4 (anion exchanger), member 1, adapter protein
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 (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.

The erythrocyte and kidney forms are different isoforms of the same protein.

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'. 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 in Red Cells

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.

Function

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 cell and conversion (by hydration catalysed by carbonic anhydrase) into a proton and a bicarbonate ion. The bicarbonate is then extruded 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.

Pathology

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]

AE1 in Alpha-Intercalated cells

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.

Function

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.

Pathology

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.

Interactions

Band 3 has been shown to interact with Carbonic anhydrase II^[5][6][7][8] and CA4.^[9]

See also

• Cluster of differentiation

References

1. ^ Alper, S. L. (2009). "Molecular physiology and genetics of Na+-independent SLC4 anion exchangers". Journal of Experimental Biology 212 (11): 1672–1683. doi:10.1242/jeb.029454. PMC 2683012. PMID 19448077. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2683012.  edit
2. ^ Hunter M (1977). "Human erythrocyte anion permeabilities measured under conditions of net charge transfer". J Physiol 268 (1): 35–49. PMC 1283651. PMID 874904. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1283651. 
3. ^ LJ Bruce; Robinson, HC; Guizouarn, H; Borgese, F; Harrison, P; King, MJ; Goede, JS; Coles, SE et al. (November 2005). "Monovalent cation leaks in human red cells caused by single amino-acid substitutions in the transport domain of the band 3 chloride-bicarbonate exchanger, AE1". Nature Genetics 37 (11): 1258–63. doi:10.1038/ng1656. PMID 16227998. 
4. ^ Jarolim p; Palek, J; Amato, D; Hassan, K; Sapak, P; Nurse, GT; Rubin, HL; Zhai, S et al. (1991). "Deletion in erythrocyte band 3 gene in malaria-resistant Southeast Asian ovalocytosis". PNAS 88 (24): 11022–11026. Bibcode 1991PNAS...8811022J. doi:10.1073/pnas.88.24.11022. PMC 53065. PMID 1722314. http://www.pnas.org/cgi/content/abstract/88/24/11022. 
5. ^ Sterling, D; Reithmeier R A, Casey J R (Dec. 2001). "A transport metabolon. Functional interaction of carbonic anhydrase II and chloride/bicarbonate exchangers". J. Biol. Chem. (United States) 276 (51): 47886–94. doi:10.1074/jbc.M105959200. ISSN 0021-9258. PMID 11606574. 
6. ^ Vince, J W; Reithmeier R A (Oct. 1998). "Carbonic anhydrase II binds to the carboxyl terminus of human band 3, the erythrocyte C1-/HCO3- exchanger". J. Biol. Chem. (UNITED STATES) 273 (43): 28430–7. doi:10.1074/jbc.273.43.28430. ISSN 0021-9258. PMID 9774471. 
7. ^ Vince, J W; Carlsson U, Reithmeier R A (Nov. 2000). "Localization of the Cl-/HCO3- anion exchanger binding site to the amino-terminal region of carbonic anhydrase II". Biochemistry (UNITED STATES) 39 (44): 13344–9. doi:10.1021/bi0015111. ISSN 0006-2960. PMID 11063570. 
8. ^ Vince, J W; Reithmeier R A (May. 2000). "Identification of the carbonic anhydrase II binding site in the Cl(-)/HCO(3)(-) anion exchanger AE1". Biochemistry (UNITED STATES) 39 (18): 5527–33. doi:10.1021/bi992564p. ISSN 0006-2960. PMID 10820026. 
9. ^ Sterling, Deborah; Alvarez Bernardo V, Casey Joseph R (Jul. 2002). "The extracellular component of a transport metabolon. Extracellular loop 4 of the human AE1 Cl-/HCO3- exchanger binds carbonic anhydrase IV". J. Biol. Chem. (United States) 277 (28): 25239–46. doi:10.1074/jbc.M202562200. ISSN 0021-9258. PMID 11994299. 

External links

• Diego blood group system at BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH
• MeSH Band+3+Protein
• MeSH Chloride-Bicarbonate+Antiporters

Further reading

• Tanner MJ (1993). "Molecular and cellular biology of the erythrocyte anion exchanger (AE1)". Semin. Hematol. 30 (1): 34–57. PMID 8434259. 
• Chambers EJ, Askin D, Bloomberg GB, et al. (1998). "Studies on the structure of a transmembrane region and a cytoplasmic loop of the human red cell anion exchanger (band 3, AE1)". Biochem. Soc. Trans. 26 (3): 516–20. PMID 9765907. 
• Inaba M (2002). "[Band 3: expanding knowledge on its functions]". Seikagaku 73 (12): 1431–5. PMID 11831035. 
• Tanner MJ (2002). "Band 3 anion exchanger and its involvement in erythrocyte and kidney disorders". Curr. Opin. Hematol. 9 (2): 133–9. doi:10.1097/00062752-200203000-00009. PMID 11844997. 
• Shayakul C, Alper SL (2004). "Defects in processing and trafficking of the AE1 Cl-/HCO3- exchanger associated with inherited distal renal tubular acidosis". Clin. Exp. Nephrol. 8 (1): 1–11. doi:10.1007/s10157-003-0271-x. PMID 15067510.