Recently the sequence of a number of different proteins, that all seem to be
transmembrane channel proteins, has been found to be highly related [1,2,3,4].
These proteins are listed below.
Mammalian major intrinsic protein (MIP). MIP is the major component of lens
fiber gap junctions. Gap junctions mediate direct exchange of ions and
small molecule from one cell to another.
Mammalian aquaporins . 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.
Soybean nodulin-26, a major component of the peribacteroid membrane induced
during nodulation in legume roots after Rhizobium infection.
Plants tonoplast intrinsic proteins (TIP). There are various isoforms of
TIP: α (seed), γ, 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.
Bacterial glycerol facilitator protein (gene glpF), which facilitates the
movement of glycerol across the cytoplasmic membrane.
Yeast FPS1, a glycerol uptake/efflux facilitator protein.
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.
Yeast hypothetical protein YFL054c.
A hypothetical protein from the pepX region of lactococcus lactis.
The MIP family proteins seem to contain six transmembrane segments. Computer
analysis shows that these protein probably arose by a tandem, intragenic
duplication event from an ancestral protein that contained three transmembrane
segments. As a signature pattern we selected a well conserved region which is
located in a probable cytoplasmic loop between the second and third
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