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)

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

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

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