Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.24.59 (MIP)
 4,906 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two recently cloned water channels, CHIP28 and WCH-CD, are homologous to MIP26, an integral membrane channel-forming protein found in lens fiber plasma membranes. CHIP28 is found in basolateral and apical plasma membranes of kidney proximal tubules and thin descending limbs of Henle, whereas WCH-CD is apically located in collecting duct principal cells. So far, the putative water channel that may be responsible for the high constitutive permeability of principal cell basolateral membranes has not been identified. Interestingly, freeze-fracture electron microscopy has shown that characteristic orthogonal arrays of intramembrane particles (OAPs) are found on the basolateral plasma membranes of collecting duct principal cells, and that morphologically identical OAPs present in lens fiber cell plasma membranes contain the protein MIP26. Similar OAPs have also been detected on plasma membranes of other cell types including gastric parietal cells, astroglial cells and skeletal muscle fibers. By indirect immunofluorescence, western blotting and northern blotting, MIP26 was found only in lens fibers. In addition, functional studies on reconstituted and oocyte-expressed MIP26 excluded the possibility that MIP26 might be a basolateral water channel in the kidney. However, a polyclonal antibody raised against skeletal muscle sarcolemmal vesicles, which are enriched in OAPs, produced an intense staining of principal cell basolateral plasma membranes in kidney collecting duct and immunoprecipitated a 28 kDa protein from kidney papilla. The immunoprecipitated protein from papilla was not recognized by anti-CHIP28 or anti-MIP26 antibodies, indicating that principal cell basolateral membranes contain a novel member of the CHIP/MIP family. Because this antibody also stained brain astrocyte end feet, which are enriched in OAPs, it is possible that the 28 kDa protein is related to these structures. We conclude that OAPs probably contain related but distinct proteins that may have different membrane channel functions in different cell types.
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PMID:A 28 kDa sarcolemmal antigen in kidney principal cell basolateral membranes: relationship to orthogonal arrays and MIP26. 752 41

The human AQP2 (collecting duct water channel, aquaporin 2) gene encodes a 271 amino acid protein and is a member of the MIP (major intrinsic protein of lens fiber) gene family. Using two-color fluorescence in situ hybridization on high-resolution R-banded chromosomes and human genomic DNA clones for AQP2 and MIP as probes, we found that both genes mapped closely within the human chromosome region 12q13.
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PMID:Human AQP2 and MIP genes, two members of the MIP family, map within chromosome band 12q13 on the basis of two-color FISH. 752 61

A cDNA encoding rat AQP3, a water channel and a member of the MIP family, that is expressed predominantly in kidney medulla and colon was cloned recently. To determine the structure, tissue distribution, and chromosomal localization of the human AQP3 gene, we screened a human kidney cDNA library with rat AQP3 probe and isolated a cDNA coding for human AQP3 protein. The deduced amino acid sequence of human AQP3 was 91% identical to rat AQP3. Human AQP3 mRNA was expressed in colon, kidney, liver, pancreas, lung, peripheral leukocytes, spleen, and prostate. The human AQP3 gene was mapped to 7q36.2-q36.3 by chromosome fluorescence in situ hybridization.
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PMID:Structure and chromosomal localization of a human water channel (AQP3) gene. 755 5

The vacuolar membrane (tonoplast) of higher plant cells contains an abundant 27 kDa protein called TIP (tonoplast intrinsic protein) that occurs in different isoforms and belongs to a large family of homologous channel-like proteins found in bacteria, plants and animals. In the present study, we identified and characterized the function of gamma-TIP from Arabidopsis thaliana by expression of the protein in Xenopus oocytes. gamma-TIP increased the osmotic water permeability of oocytes 6- to 8-fold, to values in the range 1-1.5 x 10(-2) cm/s. Similar results were obtained with the homologous human erythrocyte protein CHIP28, recently identified as the erythrocyte water channel. The bacterial homolog GlpF did not affect the osmotic water permeability of oocytes, but facilitated glycerol uptake, in accordance with its known function. By contrast, gamma-TIP did not promote glycerol permeability. Voltage clamp experiments provided evidence showing that gamma-TIP induced no electrogenic ion transport in oocytes, especially during osmotic challenge that resulted in massive transport of water. These results allow us to conclude that the various protein members of the MIP family have unique and specific transport functions and that the plant protein gamma-TIP likely functions as a water specific channel in the vacuolar membrane.
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PMID:The vacuolar membrane protein gamma-TIP creates water specific channels in Xenopus oocytes. 850 61

In a recent work, we showed that the aquaporins 1 (AQP1) are permeable to certain small solutes such as glycerol. Here, we have further investigated the permeation pathway of glycerol through human AQP1 (hAQP1) by the use of mutants (C189S, H180A, H209A) and inhibitors such as P-chloromercuribenzene sulphonate (pCMBS), CuSO4 or phloretin, in comparison with other AQP-MIP (where MIP denotes major intrinsic protein) proteins: hAQP2, plant water channel gammaTIP and bacterial glycerol permease facilitator, GlpF. Glycerol movements were measured in Xenopus laevis oocytes. Apparent glycerol permeability coefficients (P'gly) were calculated from the rates of oocyte swelling upon exposure to an isoosmotic medium containing an inwardly directed gradient of glycerol and from [3H]glycerol uptake measurements. Similar P'gly values were obtained for hAQP1 and hAQP2 6 to 8 times greater than control indicating that hAQP2 also transports glycerol. P'gly of hAQP2-injected oocytes was pCMBS and CuSO4 sensitive. In contrast, the P'gly value of gammaTIP was close to that of control, indicating that gammaTIP does not transport glycerol. The hAQP1-C189S, -H180A and -H209A mutants gave P'gly values similar to those obtained for wild hAQP1, indicating that these mutations did not affect glycerol movements. However, the H209A mutant has an osmotic water permeability coefficient (Pf) value decreased by 50%. The inhibitory effect pCMBS on P'gly was maintained for the 2 His mutants and, more interestingly, was also conserved for the C189S mutant. CuSO4 significantly inhibited P'gly of oocytes expressing hAQP1, hAQP1-C189S, -H180A, and -H209A mutants and had no effect on P'gly of GlpF-injected oocytes. Phloretin was shown to inhibit by around 80% the glycerol fluxes of wild and mutant hAQP1, hAQP2 and to fully inhibit glycerol uptake in GlpF-injected oocytes.
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PMID:Glycerol permeability of mutant aquaporin 1 and other AQP-MIP proteins: inhibition studies. 858 35

Xenopus laevis oocytes are widely used as an expression system for plasma membrane proteins, achieved by cytoplasmic microinjection of messenger RNA. In the present study, we propose an alternative system allowing functional insertion of exogenous proteins into the plasma membrane of Xenopus oocytes. We microinjected proteoliposome suspensions into the cytoplasm and then analyzed membrane protein function. The proteins used in this work were members of the MIP family: the human erythrocyte water channel aquaporin 1 (AQP1), the major intrinsic protein (MIP26) from bovine eye lens and a 25 kDa polypeptide (P25) from a water shunting complex found in the digestive tract of an homopteran sap-sucking insect (Cicadella viridis). Proteoliposomes containing either AQP1, MIP26, or P25 were injected into Xenopus oocytes. The subsequent insertion of these proteins into the plasma membrane of oocytes was demonstrated by immunocytochemistry. Oocytes microinjected with either AQP1 or P25-proteoliposomes exhibited significantly increased osmotic membrane water permeabilities (Pf = 3.16 +/- 026 and 4.03 +/- 0.26 x 10(-3) cm/second, respectively) compared to those measured for oocytes injected with liposomes alone or with MIP26-proteoliposomes (Pf = 1.39 +/- 0.07 and 1.44 +/- 0.10 x 10(-3) cm/second, respectively). These effects were inhibited by HgCl2 in a reversible manner. Arrhenius activation energies of water transfer were low when AQP1 or P25 were present in oocyte plasma membranes (Ea = 2.29 and 3.01 kcal/mol, respectively, versus Ea = 11.75 kcal/mol for liposome injected oocytes). The properties observed here for AQP1 are identical to those widely reported following AQP1 cRNA expression in oocytes. From the present study, we conclude that: (1) exogenous plasma membrane proteins incorporated into liposomes and microinjected into the cytoplasm of Xenopus oocytes are subsequently found in the plasma membrane of the oocytes in a functional state; and (2) in this system, the P25 polypeptide from the MIP family found in the digestive tract of Cicadella viridis exhibits properties similar to those described for the archetype of water channels AQP1, and thus is a new member of the aquaporin family.
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PMID:Incorporation of proteins into (Xenopus) oocytes by proteoliposome microinjection: functional characterization of a novel aquaporin. 879 18

A 1.8-kb cDNA clone (designed hKID, gene symbol AQP2L) with homology to the aquaporins was isolated from a human kidney cDNA library. The longest open reading frame of 846 bp encoded a 282-amino-acid hydrophobic protein that contained the conserved NPA motifs of MIP family members. Cell-free translation produced a nonglycosylated protein migrating at 29 kDa. Amino acid alignment showed the greatest homology of hKID to human MIP (48% identity) and AQP-2 (52%), with lesser homology to human MIWC (AQP-4, 34%), CHIP28 (AQP-1, 38%), and GLIP (AQP-3, 22%). Northern blot analysis revealed a 2.2-kb transcript expressed only in human kidney. PCR/Southern blot analysis of human kidney cDNA using primers flanking the hKID coding sequence revealed expression of a full-length mRNA and short transcripts with partial exon 1 and partial exon 4 deletions. Expression of hKID cRNA in Xenopus oocytes did not increase glycerol or urea permeability, but increased osmotic water permeability from (2.8 +/- 0.5) x 10(-4) to (7.4 +/- 0.7) x 10(-4) cm/s (10 degrees C) in a mercurial-sensitive manner. Sequence comparison of hKID cDNA with a cloned 21-kb genomic DNA indicated three introns (lengths 0.7, 0.25, and 0.4 kb) separating four exons with boundaries at amino acids 121, 174, and 201. The hKID promoter was identified and contained TATA, SP1, E-box, and AP1 and AP2 elements; primer extension revealed hKID transcription initiation 654 bp upstream from the translational initiation site. Genomic Southern blot indicated a single-copy hKID gene. PCR analysis of a human/rodent somatic hybrid panel localized the hKID gene to chromosome 12. Chromosomal fluorescence in situ hybridization mapped the hKID (AQP2L) gene to chromosome locus 12q13, the same location as the AQP. 2 and MIP genes. The high sequence homology, similar genomic structure, and identical chromosomal loci of hKID, MIP, and AQP-2 suggest a MIP family gene cluster at chromosome locus 12q13. Further work is needed to establish the physiological significance of hKID.
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PMID:cDNA cloning and gene structure of a novel water channel expressed exclusively in human kidney: evidence for a gene cluster of aquaporins at chromosome locus 12q13. 881 90

This paper gives an overview of recent findings regarding erythrocyte transport. The main transport systems in erythrocyte are Na+, K(+)-ATPase, Ca(2+)-ATPase, anion transport by band 3 protein, water channel and glucose transporter. The kinetics of Na+, K(+)-ATPase had been investigated in detail in several studies and these findings were briefly summarized. The accumulated studies in Ca(2+)-ATPase suggest that the ATPase is also E1/E2 type enzyme. The band 3 protein is most densely distributed protein in the erythrocyte membrane. The anion exchange through band 3 protein is indispensable for CO2 transport from CO2 generating tissues to the lung. The development of molecular biology enabled to discover water channel. The existence of water channel explains the swift movement of water through erythrocyte membrane. The gene for water channel of erythrocyte is designated as AQP1 and is one of gene family, MIP, consisting of 20 genes. The glucose transporter was also identified in the erythrocyte membrane and was named as GLUT1. The transporters involved in Na+, K(+)-cotransport, Na(+)-Li+ countertransport, and Gardos effect remain to be identified.
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PMID:[Characteristic feature in transport of erythrocyte membrane]. 889 May 63

1. It now appears that when water crosses an endothelium which is not fenestrated, or an epithelium with tight junctions, it does so rapidly, and with low energy cost, only if the cell membrane contains an adequate number of specific water channels, encoded by one of at least six different genes. 2. The water channel genes so far cloned encode a series of integral membrane proteins called aquaporins, all of approximately 30 kDa (265-282 amino acids), in the unglycosylated state. All but one (AQP3) are specific water channels and all but one (AQP4) are inactivated by mercurial compounds. 3. Aquaporin 0 is the major (60%) intrinsic protein (MIP) of lens fibre cells of the eye. Mutations in this gene are associated with cataract formation in mice. 4. Aquaporin 1, also called CHIP-28, exists in the membrane as a homotetramer, and is present in red blood cells, the choroid plexus, the proximal tubule and descending limb of the loop of Henle in the kidney as well as in many other sites. Surprisingly, no pathological consequence is known in patients lacking a functional AQP1 gene. 5. Aquaporin 2, also called WCH-CD, is the water channel of the principal cell of the cortical and medullary collecting duct, and is located in cytoplasmic vesicles unless arginine vasopressin is acting, when it is translocated to the apical membrane by synaptobrevins or vesicle associated membrane protein 2 (VAMP2). Lack of a functional AQP2 gene leads to a rare form of nephrogenic diabetes insipidus. 6. Aquaporins 3, 4, and 5 are located in many tissues-AQP3 and AQP4 being in the basolateral membrane of the renal cortical and medullary principal cell, as well as in the gastrointestinal tract (AQP3) and the brain (AQP4). 7. Four sequences are known for urea transporters HUT11-the urea transporter of the human red cell membrane, and HUT2, rUT2, rbUT2-the arginine vasopressin inducible urea transporters of the human, rat and rabbit kidney. They are specifically permeable to urea, not to water, and are claimed to be inhibited by phloretin. 8. The water channel proteins contain six membrane-spanning regions, whilst the urea transporters are thought to contain at least 10 membrane spanning segments. 9. Very little work has examined the ontogeny of these proteins, except in the rat, and virtually nothing is known of the expression of these genes in pregnancy or in any disorder of fluid balance in the mother or foetus.
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PMID:Water channels and urea transporters. 904 98

A new member of water channels has been identified from rat testis. This gene, termed aquaporin 8 (AQP8), encoded a 263-amino-acid protein that contained the conserved NPA motifs of MIP family proteins. AQP8 has amino acid sequence identity with other aquaporins (approximately 35%) and highest with a plant water channel, AQP-gamma TIP (39%), suggesting that AQP8 is a unique member in mammalian aquaporins. The expression of AQP8 in Xenopus oocytes stimulated the osmotic water permeability (Pr) 8.5 folds. The increase of Pr was inhibited with 0.3 mM mercury chloride by 55%, which was reversed with mercaptoethanol. The Arrhenius activation energy for the stimulated water permeability was low (5.1 kcal/mol). AQP8 did not facilitate glycerol transport. Northern blot analysis revealed a 1.5-kb transcript of AQP8 abundantly in testis and slightly in liver. In situ hybridization of testis revealed the expression of AQP8 mRNA in all stages of spermatogenesis from primary spermatocytes to spermatids in seminiferous tubules. Together with previously cloned AQP7, AQP8 may also play an important role in spermatogenesis. The unexpected complexity of the presence of two aquaporins in testis may call for the further analysis of the role of aquaporins in the reproduction biology.
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PMID:Cloning and functional expression of a second new aquaporin abundantly expressed in testis. 929 32


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