Passive transport by Aquaporins (Homo sapiens)

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5, 7, 11, 24, 25, 40...1, 6, 8, 13-15, 20...1, 6, 8, 14, 20...1-4, 6, 8...531-4, 6, 8...1, 6, 14, 20, 28...1, 6, 8, 13-15, 20...53transport vesiclecytosolFl- H2OAQP0,1,2,3,4,5,7,8,9,10,11AQP8 AQP1 AQP6 p-S256-AQP2 AQP10 AQP7 GlycerolMIP H2OAQP9,10HNO3 AQP3 AQP3,7,9,10AQP4 UreaAQP10 AQP9 I- AQP5 AQP11 Br- Fl- AQP10 Br- AQP7 AQP3 Cl- AQP9 Cl- I- Anions transportedby Aquaporin-6glycerolHNO3 UreaAnions transportedby Aquaporin-6AQP6 tetramerAQP9


Description

Aquaporins (AQP's) are six-pass transmembrane proteins that form channels in membranes. Each monomer contains a central channel formed in part by two asparagine-proline-alanine motifs (NPA boxes) that confer selectivity for water and/or solutes. The monomers assemble into tetramers. Most aquaporins (i.e. AQP0/MIP, AQP1, AQP2, AQP3, AQP4, AQP5, AQP7, AQP8, AQP9, AQP10) passively transport water into and out of cells according to the osmotic gradient across the membrane. Four aquaporins (the aquaglyceroporins AQP3, AQP7, AQP9, AQP10) conduct glycerol, three aquaporins (AQP7, AQP9, AQP10) conduct urea, and one aquaporin (AQP6) conducts anions, especially nitrate. AQP8 also conducts ammonia in addition to water.
AQP11 and AQP12, classified as group III aquaporins, were identified as a result of the genome sequencing project and are characterized by having variations in the first NPA box when compared to more traditional aquaporins. Additionally, a conserved cysteine residue is present about 9 amino acids downstream from the second NPA box and this cysteine is considered indicative of group III aquaporins. Purified AQP11 incorporated into liposomes showed water transport. Knockout mice lacking AQP11 had fatal cyst formation in the proximal tubule of the kidney. Exogenously expressed AQP12 showed intracellular localization. AQP12 is expressed exclusively in pancreatic acinar cells.
Aquaporins are important in fluid and solute transport in various tissues. In adipocytes, glycerol generated by triglyceride hydrolysis is exported by AQP7 and is imported by liver cells via AQP9. AQP1 plays a role in forming cerebrospinal fluid and AQP1, AQP4, and AQP9 appear to be important in maintaining fluid balance in the brain. AQP0, AQP1, AQP3, AQP4, AQP8, AQP9, and AQP11 play roles in the physiology of the hepatobiliary tract. In the kidney, water and solutes are passed out of the bloodstream and into the proximal tubule via the slit-like structure formed by nephrin in the glomerulus. Water is reabsorbed from the filtrate during its transit through the proximal tubule, the descending loop of Henle, the distal convoluted tubule, and the collecting duct. Aquaporin-1 (AQP1) in the proximal tubule and the descending thin limb of Henle is responsible for about 90% of reabsorption (as estimated from mouse knockouts of AQP1). AQP1 is located on both the apical and basolateral surface of epithelial cells and thus transports water through the epithelium and back into the bloodstream. In the collecting duct epithelial cells have AQP2 on their apical surfaces and AQP3 and AQP4 on their basolateral surfaces to transport water across the epithelium. The permeability of the epithelium is regulated by vasopressin, which activates a signaling cascade leading to the phosphorylation of AQP2 and its translocation from intracellular vesicles to the apical membrane of collecting duct cells.
Here, three views of aquaporin-mediated transport have been annotated: a generic view of transport mediated by the various families of aquaporins independent of tissue type, a view of the role of specific aquaporins in maintenance of renal water balance, and a view of the role of specific aquaporins in glycerol transport from adipocytes to the liver. View original pathway at:Reactome.

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Bibliography

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History

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CompareRevisionActionTimeUserComment
115085view17:03, 25 January 2021ReactomeTeamReactome version 75
113527view12:00, 2 November 2020ReactomeTeamReactome version 74
112725view16:12, 9 October 2020ReactomeTeamReactome version 73
101641view11:50, 1 November 2018ReactomeTeamreactome version 66
101177view21:37, 31 October 2018ReactomeTeamreactome version 65
100703view20:10, 31 October 2018ReactomeTeamreactome version 64
100253view16:55, 31 October 2018ReactomeTeamreactome version 63
99806view15:20, 31 October 2018ReactomeTeamreactome version 62 (2nd attempt)
93844view13:40, 16 August 2017ReactomeTeamreactome version 61
93400view11:22, 9 August 2017ReactomeTeamreactome version 61
88086view09:15, 26 July 2016RyanmillerOntology Term : 'transport pathway' added !
88085view09:14, 26 July 2016RyanmillerOntology Term : 'water transport pathway' added !
88084view09:12, 26 July 2016RyanmillerOntology Term : 'regulatory pathway' added !
86485view09:19, 11 July 2016ReactomeTeamreactome version 56
83120view10:01, 18 November 2015ReactomeTeamVersion54
81770view10:17, 26 August 2015ReactomeTeamVersion53
77006view08:30, 17 July 2014ReactomeTeamFixed remaining interactions
76711view12:07, 16 July 2014ReactomeTeamFixed remaining interactions
76037view10:09, 11 June 2014ReactomeTeamRe-fixing comment source
75746view11:23, 10 June 2014ReactomeTeamReactome 48 Update
75096view14:04, 8 May 2014AnweshaFixing comment source for displaying WikiPathways description
74743view08:49, 30 April 2014ReactomeTeamReactome46
42093view21:56, 4 March 2011MaintBotAutomatic update
39903view05:55, 21 January 2011MaintBotNew pathway

External references

DataNodes

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NameTypeDatabase referenceComment
AQP0,1,2,3,4,5,7,8,9,10,11ComplexR-HSA-507884 (Reactome)
AQP1 ProteinP29972 (Uniprot-TrEMBL)
AQP10 ProteinQ96PS8 (Uniprot-TrEMBL)
AQP11 ProteinQ8NBQ7 (Uniprot-TrEMBL)
AQP3 ProteinQ92482 (Uniprot-TrEMBL)
AQP3,7,9,10ComplexR-HSA-507882 (Reactome)
AQP4 ProteinP55087 (Uniprot-TrEMBL)
AQP5 ProteinP55064 (Uniprot-TrEMBL)
AQP6 ProteinQ13520 (Uniprot-TrEMBL)
AQP6 tetramerComplexR-HSA-432253 (Reactome) The formation of homotetramers by Aquaporin-6 (AQP6) is inferred from human AQP1, AQP2, AQP3, AQP4, and AQP5.
AQP7 ProteinO14520 (Uniprot-TrEMBL)
AQP8 ProteinO94778 (Uniprot-TrEMBL)
AQP9 ProteinO43315 (Uniprot-TrEMBL)
AQP9,10ComplexR-HSA-507881 (Reactome)
Anions transported by Aquaporin-6ComplexR-HSA-R-ALL-879865 (Reactome)
Anions transported by Aquaporin-6ComplexR-HSA-R-ALL-879874 (Reactome)
Br- MetaboliteCHEBI:15858 (ChEBI)
Cl- MetaboliteCHEBI:17996 (ChEBI)
Fl- MetaboliteCHEBI:17051 (ChEBI)
GlycerolMetaboliteCHEBI:17754 (ChEBI)
H2OMetaboliteCHEBI:15377 (ChEBI)
HNO3 MetaboliteCHEBI:48107 (ChEBI)
I- MetaboliteCHEBI:16382 (ChEBI)
MIP ProteinP30301 (Uniprot-TrEMBL)
UreaMetaboliteCHEBI:16199 (ChEBI)
glycerolMetaboliteCHEBI:17754 (ChEBI)
p-S256-AQP2 ProteinP41181 (Uniprot-TrEMBL)

Annotated Interactions

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SourceTargetTypeDatabase referenceComment
AQP0,1,2,3,4,5,7,8,9,10,11mim-catalysisR-HSA-507868 (Reactome)
AQP0,1,2,3,4,5,7,8,9,10,11mim-catalysisR-HSA-507870 (Reactome)
AQP3,7,9,10mim-catalysisR-HSA-507869 (Reactome)
AQP3,7,9,10mim-catalysisR-HSA-507871 (Reactome)
AQP6 tetramermim-catalysisR-HSA-432034 (Reactome)
AQP6 tetramermim-catalysisR-HSA-432036 (Reactome)
AQP9,10mim-catalysisR-HSA-507873 (Reactome)
AQP9,10mim-catalysisR-HSA-507875 (Reactome)
Anions transported by Aquaporin-6ArrowR-HSA-432034 (Reactome)
Anions transported by Aquaporin-6ArrowR-HSA-432036 (Reactome)
Anions transported by Aquaporin-6R-HSA-432034 (Reactome)
Anions transported by Aquaporin-6R-HSA-432036 (Reactome)
GlycerolArrowR-HSA-507869 (Reactome)
GlycerolR-HSA-507871 (Reactome)
H2OArrowR-HSA-507868 (Reactome)
H2OArrowR-HSA-507870 (Reactome)
H2OR-HSA-507868 (Reactome)
H2OR-HSA-507870 (Reactome)
R-HSA-432034 (Reactome) Aquaporin-6 (AQP6) passively transports anions across membranes. Rat AQP6 has been shown to transport anions, with the highest permeability for nitrate, the lowest permeability for fluoride, and low permeability for water. In rat AQP6 is expressed in the acid-secreting type-A intercalated cells of renal ducts where it co-localizes with the proton-ATPase in the membranes of intracellular vesicles. AQP6 is gated by low pH.
R-HSA-432036 (Reactome) Aquaporin-6 (AQP6) passively transports anions across membranes. Rat AQP6 has been shown to transport anions, with the highest permeability for nitrate, the lowest permeability for fluoride, and low permeability for water. In rat AQP6 is expressed in the acid-secreting type-A intercalated cells of renal ducts where it co-localizes with the proton-ATPase in the membranes of intracellular vesicles. AQP6 is gated by low pH.
R-HSA-507868 (Reactome) Aquaporin-0 (AQP0, also known as MIP), AQP1, AQP2, AQP3, AQP4, AQP5, AQP7, AQP8, AQP9, and AQP10 are 6-pass transmembrane proteins that passively transport water across the plasma membrane according to the concentration gradient. Each molecule contains a water channel and subunits assemble into homotetramers. In principle water can move in either direction through an aquaporin, however in vivo flow may occur in only one direction. Conductance of water by AQP0 and AQP11 are low relative to other aquaporins.
R-HSA-507869 (Reactome) Aquaporin-3 (AQP3), AQP7, AQP9, and AQP10 are 6-pass transmembrane proteins that passively transport glycerol across the plasma membrane through a pore in each subunit of a homotetramer.
R-HSA-507870 (Reactome) Aquaporin-0 (AQP0, also known as MIP), AQP1, AQP2, AQP3, AQP4, AQP5, AQP7, AQP8, AQP9, and AQP10 are 6-pass transmembrane proteins that passively transport water across the plasma membrane according to the concentration gradient. Each molecule contains a water channel and subunits assemble into homotetramers. In principle water can move in either direction through an aquaporin, however in vivo flow may occur in only one direction. Conductance of water by AQP0 and AQP11 are low relative to other aquaporins.
R-HSA-507871 (Reactome) Aquaporin-3 (AQP3), AQP7, AQP9, and AQP10 are 6-pass transmembrane proteins that passively transport glycerol across the plasma membrane through a pore in each subunit of a homotetramer.
R-HSA-507873 (Reactome) Aquaporin-9 (AQP9) and AQP10 are 6-pass transmembrane proteins that passively transport urea across the plasma membrane through a pore in each subunit of a homotetramer.
R-HSA-507875 (Reactome) Aquaporin-9 (AQP9) and AQP10 are 6-pass transmembrane proteins that passively transport urea across the plasma membrane through a pore in each subunit of a homotetramer.
UreaArrowR-HSA-507873 (Reactome)
UreaArrowR-HSA-507875 (Reactome)
UreaR-HSA-507873 (Reactome)
UreaR-HSA-507875 (Reactome)
glycerolArrowR-HSA-507871 (Reactome)
glycerolR-HSA-507869 (Reactome)
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