band 3 anion transport protein 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. slc4a1available structurespdbortholog search: pdbe rcsb list of pdb id codes1bh7, 1bnx, 1btq, 1btr, 1bts, 1btt, 1bzk, 1hyn, 3btb, 2bta, 2btb, 4ky9, 4yzfidentifiersaliasesslc4a1, solute carrier family 4 (anion exchanger), member 1 (diego blood group), ae1, bnd3, cd233, di, empb3, epb3, fr, rta1a, sw, wd, wd1, wr, chc, sao, sph4, solute carrier family 4 member 1 (diego blood group)external idsomim: 109270 mgi: 109393 homologene: 133556 genecards: slc4a1 gene location (human)chr.chromosome 17 (human)band17q21.31start44,248,390 bpend44,268,141 bpgene location (mouse)chr.chromosome 11 (mouse)band11 66.29 cm|11 dstart102,239,650 bpend102,257,029 bprna expression patternbgeehumanmouse (ortholog)top expressed incancellous bonebone marrowbone marrow cellsrenal medullabloodkidneymonocytekidney tubulevena cavaglomerulustop expressed inbloodinternal carotid arterybody of femurexternal carotid arteryyolk sacendocardial cushionspleenbelly cordfossaatriummore reference expression databiogpsmore reference expression datagene ontologymolecular function protein homodimerization activity protein-membrane adaptor activity chloride transmembrane transporter activity transporter activity anion transmembrane transporter activity bicarbonate transmembrane transporter activity protein binding ankyrin binding inorganic anion exchanger activity sodium:bicarbonate symporter activity hemoglobin binding cellular component integral component of membrane blood microparticle membrane cortical cytoskeleton plasma membrane integral component of plasma membrane basolateral plasma membrane extracellular exosome z disc cytoplasmic side of plasma membrane biological process anion transport bicarbonate transport cellular ion homeostasis chloride transport ion transport regulation of intracellular ph anion transmembrane transport chloride transmembrane transport sodium ion transmembrane transport transport glycolytic process blood coagulation plasma membrane phospholipid scrambling negative regulation of urine volume ph elevation erythrocyte development protein localization to plasma membrane sources:amigo / quickgoorthologsspecieshumanmouseentrez652120533ensemblensg00000004939ensmusg00000006574uniprotp02730p04919refseq (mrna)nm_000342nm_011403refseq (protein)np_000333np_035533location (ucsc)chr 17: 44.25 – 44.27 mbchr 11: 102.24 – 102.26 mbpubmed searchwikidataview/edit humanview/edit mouse solute carrier family 4 (anion exchanger), member 1, adapter proteinidentifierssymbolslc4a1apncbi gene22950hgnc13813omim602655refseqnm_018158uniprotp02730other datalocuschr. 2 p23.3search forstructuresswiss-modeldomainsinterpro band 3 anion transport protein is a phylogenetically-preserved transport protein responsible for mediating the exchange of chloride (cl−) with bicarbonate (hco3−) across plasma membranes. functionally similar members of the ae clade are ae2 and ae3. function 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: 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 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. 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. the kidney 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 (type 1) 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 antigen system (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 and southeast asian ovalocytosis. interactions band 3 has been shown to interact with ca2 and ca4. discovery 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'.