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

17 members of MIP family from bacteria, yeast, plants and animals are compared in this review. These proteins appear to function in (1) water channels (CHIP, WCH-CD, MIWC, AQP3, gTIP, RD28, TobRB7), (2) neurogenesis (Bib), (3) small-molecule-permeating channels (MIP, AQP3, NOD, Glpf), (4) unknown function (WCH-3, AtRB7, Pea R7A, FPS1). However, the biological functions are not well established. The most conserved residues in the first and the second halves of all MIP family proteins are asparagine-proline-alanine (NPA) sequences in the loops (NPA boxes). This structural similarity may lead to functional similarity (water and/or small molecule permeation). This signature sequence for the MIP family will facilitate the identification of new protein members of this family.
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PMID:[Water channel family proteins]. 753 36

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

A new member of the aquaporin (AQP) family has been identified from rat testis. This gene, referred as aquaporin 7 (AQP7), encodes a 269-amino acid protein that contained the conserved NPA motifs of MIP family proteins. AQP7 has the amino acid sequence homology with other aquaporins ( approximately 30%), and it is highest with AQP3 (48%), suggesting that both AQP3 and AQP7 belong to a subfamily in the MIP family. Injection of AQP7-cRNA into Xenopus oocytes expressed a 26-kDa protein detected by immunoblotting. The expression of AQP7 in oocytes stimulated the osmotic water permeability by 10-fold which was not inhibited by 0.3 mM mercury chloride. The Arrhenius activation energy for the stimulated water permeability was low (2.1 kcal/mol). AQP7 also facilitated glycerol and urea transport by 5- and 9-fold, respectively. The activation energy for glycerol was also low (5.3 kcal/mol after the correction of the endogenous glycerol permeability of oocytes). Northern blot analysis revealed a 1.5-kilobase pair transcript expressed abundantly in testis. In situ hybridization of testis revealed the expression of AQP7 at late spermatids in seminiferous tubules. The immunohistochemistry of testis localized the AQP7 expression at late spermatids and at maturing sperms. AQP7 may play an important role in sperm function.
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PMID:Cloning and functional expression of a new water channel abundantly expressed in the testis permeable to water, glycerol, and urea. 925 1

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

An aquaporin-type water channel was isolated from mouse based on homology to known aquaporins. A 1447 bp cDNA was sequenced (designated AQP8) with a 783 bp open reading frame encoding a 261 amino acid hydrophobic protein which contained the conserved NPA motifs of MIP family members. Amino acid alignment showed greatest homology of AQP8 to plant water channel gamma TIP (38% identity) followed by mammalian water channels AQP4 (32%) and AQP2 (31%). Northern blot analysis indicated a 1.7 kb transcript expressed strongly in placenta > colon > liver approximately heart. RT-PCR with AQP8-specific primers and Southern blot analysis showed AQP8 transcript in the above tissues and in pancreas, lung, kidney, submandibular gland, diaphragm, testis, spleen, stomach and brain. Expression of AQP8 cRNA in Xenopus oocytes increased osmotic water permeability from (0.8 +/- 0.1) x 10(-3) cm/s to (22 +/- 3) x 10(-3) cm/s (10 degrees C) in a mercurial-sensitive manner. AQP8 was also permeable to urea but not to glycerol. Normalization for oocyte plasma membrane expression using cMyc-tagged AQP8 indicated a single channel water permeability of 8.2 x 10(-14) cm3/s. AQP8 is unique among the water channels in terms of its urea permeability and its strong expression in gastrointestinal organs, placenta and heart.
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PMID:Cloning of a novel water and urea-permeable aquaporin from mouse expressed strongly in colon, placenta, liver, and heart. 938 76

Two cDNAs encoding frog aquaporin (AQP) were cloned from a cDNA library constructed for the ventral skin of the tree frog, Hyla japonica and sequenced. One AQP (Hyla AQP-h1) consisted of 271 amino-acid residues with high homology to toad AQP-t1, Rana CHIP28 (AQP1), and rat AQP1. The other AQP (AQP-h3) consisted of 271 amino-acid residues with higher homology to mammalian AQP2 than to mammalian AQP3. The predicted amino-acid sequence contained the conserved two NPA motifs found in all MIP family members and the putative six transmembrane domains. The sequence also confers mercurial sensitivity, which is common to all the AQPs except AQP0, AQP4 and AQP7. Potential N-glycosylation sites were present at Asn-44 in AQP-h1, and at Asn-124 and Asn-125 in AQP-h3. In addition, AQP-h3 had a putative phosphorylation site by protein kinase A at Ser-255, which is identical to mammalian AQP2. In swelling assays using Xenopus oocytes, AQP-h1 facilitates water permeability, whereas AQP-h3 displayed weak water permeability. Searching for the expression of these two AQP mRNAs revealed that AQP-h1 was expressed in most tissues, whereas AQP-h3 was observed only in the ventral skin. An antibody (ST-141) against the C-terminal peptide of the AQP-h3 protein recognized a 29.0 kDa-protein with a molecular mass close to that of the Hyla AQP-h3 protein and immunostained predominantly in the abdominal pelvic skin. In pelvic skin, the label for AQP-h3 was more intense in the upper layer of the stratum granulosum and was localized to both the apical and basolateral plasma membranes of the principal cells. These findings suggest that Hyla AQP-h3 plays a pivotal role in constitutively absorbing water from ventral pelvic skin.
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PMID:Molecular and cellular characterization of a water-channel protein, AQP-h3, specifically expressed in the frog ventral skin. 1217 46

Aquaporin 0 (AQP0) was originally characterized as a membrane intrinsic protein, specifically expressed in the lens fibers of the ocular lens and designated MIP, for major intrinsic protein of the lens. Once the gene was cloned, an internal repeat was identified, encoding for the amino acids Asp-Pro-Ala, the NPA repeat. Shortly, the MIP gene family was emerging, with members being characterized in mammals, insects, and plants. Once Peter Agre's laboratory developed a functional assay for water channels, the MIP family became the aquaporin family and MIP became known as aquaporin 0. Besides functioning as a water channel, aquaporin 0 also plays a structural role, being required for maintaining the transparency and optical accommodation of the ocular lens. Mutations in the AQP0 gene in human and mice result in genetic cataracts; deletion of the MIP/AQP0 gene in mice results in lack of suture formation required for maintenance of the lens fiber architecture, resulting in perturbed accommodation and focus properties of the ocular lens. Crystallography studies support the notion of the double function of aquaporin 0 as a water channel (open configuration) or adhesion molecule (closed configuration) in the ocular lens fibers. The functions of MIP/AQP0, both as a water channel and an adhesive molecule in the lens fibers, contribute to the narrow intercellular space of the lens fibers that is required for lens transparency and accommodation.
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PMID:Structural function of MIP/aquaporin 0 in the eye lens; genetic defects lead to congenital inherited cataracts. 1909 83

Silicon (Si) is a nonessential, beneficial micronutrient for plants. It increases the plant stress tolerance in relation to its accumulation capacity. In this work, root Si transporter genes were characterized in 17 different plants and inferred for their Si-accumulation status. A total of 62 Si transporter genes (31 Lsi1 and 31 Lsi2) were identified in studied plants. Lsi1s were 261-324 residues protein with a MIP family domain whereas Lsi2s were 472-547 residues with a citrate transporter family domain. Lsi1s possessed characteristic sequence features that can be employed as benchmark in prediction of Si-accumulation status/capacity of the plants. Silicic acid selectivity in Lsi1s was associated with two highly conserved NPA (Asn-Pro-Ala) motifs and a Gly-Ser-Gly-Arg (GSGR) ar/R filter. Two NPA regions were present in all Lsi1 members but some Ala substituted with Ser or Val. GSGR filter was only available in the proposed high and moderate Si accumulators. In phylogeny, Lsi1s formed three clusters as low, moderate and high Si accumulators based on tree topology and availability of GSGR filter. Low-accumulators contained filters WIGR, AIGR, FAAR, WVAR and AVAR, high-accumulators only with GSGR filter, and moderate-accumulators mostly with GSGR but some with A/CSGR filters. A positive correlation was also available between sequence homology and Si-accumulation status of the tested plants. Thus, availability of GSGR selectivity filter and sequence homology degree could be used as signatures in prediction of Si-accumulation status in experimentally uncharacterized plants. Moreover, interaction partner and expression profile analyses implicated the involvement of Si transporters in plant stress tolerance.
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PMID:Genome-wide exploration of silicon (Si) transporter genes, Lsi1 and Lsi2 in plants; insights into Si-accumulation status/capacity of plants. 2814 59