Aquaporin-like <p>A number of transmembrane (TM) channel proteins can be grouped togetheron the basis of sequence similarities [<cite idref="PUB00001006"/>, <cite idref="PUB00003816"/>, <cite idref="PUB00005368"/>, <cite idref="PUB00005428"/>, <cite idref="PUB00000835"/>].</p><p>These include:<ul><li>Mammalian major intrinsic protein (MIP). MIP is the major component of lens fibre gap junctions.</li><li>Mammalian aquaporins [<cite idref="PUB00005428"/>]. These proteins form water-specific channels that provide the plasma membranes of red cells and kidney proximal and collecting tubules with high permeability to water, thereby permitting water to move in the direction of an osmotic gradient.</li><li>Soybean nodulin-26, a major component of the peribacteroid membrane induced during nodulation in legume roots after Rhizobium infection.</li><li>Plants tonoplast intrinsic proteins (TIP). There are various isoforms of TIP: alpha (seed), gamma, Rt (root), and Wsi (water-stress induced). These proteins may allow the diffusion of water, amino acids and/or peptides from the tonoplast interior to the cytoplasm.</li><li>Bacterial glycerol facilitator protein (gene glpF), which facilitates the movement of glycerol across the cytoplasmic membrane.</li><li> <taxon tax_id="602">Salmonella typhimurium</taxon> propanediol diffusion facilitator (gene pduF).</li><li>Yeast FPS1, a glycerol uptake/efflux facilitator protein.</li><li>Drosophila neurogenic protein 'big brain' (bib). This protein may mediate intercellular communication; it may functions by allowing the transport of certain molecules(s) and thereby sending a signal for an exodermal cell to become an epidermoblast instead of a neuroblast.</li><li>Yeast hypothetical protein YFL054c.</li><li>A hypothetical protein from the pepX region of <taxon tax_id="1358">Lactococcus lactis</taxon>.</li></ul> </p><p> The structures of various members of the MIP family have been determined by means of X-ray diffraction [<cite idref="PUB00028718"/>, <cite idref="PUB00053662"/>, <cite idref="PUB00025063"/>], revealing the fold to comprise a right-handed bundle of 6 transmembrane (TM) alpha-helices [<cite idref="PUB00028718"/>, <cite idref="PUB00053662"/>, <cite idref="PUB00025063"/>]. Similarities in the N-and C-terminal halves of the molecule suggest that the proteins may have arisen through tandem, intragenic duplication of an ancestral protein that contained 3 TM domains [<cite idref="PUB00005368"/>]. </p><p>Some of the proteins in this group are responsible for the molecular basis of the blood group antigens, surface markers on the outside of the red blood cell membrane. Most of these markers are proteins, but some are carbohydrates attached to lipids or proteins [<cite idref="PUB00020601"/>]. Aquaporin-CHIP (Aquaporin 1) belongs to the Colton blood group system and is associated with Co(a/b) antigen.</p>This entry represents the aquaporin-like structural domain.