Major intrinsic proteins are a large family

Protein family

A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....

 of transmembrane protein channels that are grouped together on the basis of sequence similarities. Proteins from this family exhibit essentially two distinct types of channel properties: (1) specific water
transport by the aquaporin

Aquaporin

Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....

s, and (2) small neutral solutes
transport, such as glycerol by the glycerol facilitators.

Examples

MIP family includes the following channels:

• Mammalian major intrinsic protein (MIP). MIP is the major component of lens fibre gap junctions.
• Mammalian aquaporin
  Aquaporin
  Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....
  
  s. These proteins form water- specific channels that provide the plasma membranes of red cells and kidney prox imal 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 : 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..
• Bacterial glycerol facilitator protein (gene glpF), which facilitates the movement of glycerol across the cytoplasmic membrane.
• Salmonella typhimurium propanediol diffusion fac ilitator (gene pduF).
• Yeast FPS1, a glycerol uptake/efflux facilitator protein.
• Drosophila neurogenic protein 'big brain' (bib). This protein may mediate in tercellular communication; it may functions by allowing the transport of certain molecules(s) and thereby sending a signal for an exodermal cell to become an ep idermoblast instead of a neuroblast.
• Yeast hypothetical protein YFL054c.
• A hypothetical protein from the pepX region of Lactococcus lactis
  Lactococcus lactis
  Lactococcus lactis is a Gram-positive bacterium used extensively in the production of buttermilk and cheese, but has recently also become famous as the first genetically modified organism to be used alive for the treatment of human disease. L...
  
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Structure

MIP family proteins are thought to contain 6 TM domains. Sequence analysis suggests that the proteins may have arisen through tandem, intragenic duplication from an ancestral protein that contained 3 TM domains.

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. Aquaporin-CHIP (Aquaporin 1) belongs to the Colton blood group system and is associated with Co(a/b) antigen.

Human proteins containing this domain

AQP1

Aquaporin 1

AQP1 is a widely expressed water channel, whose physiological function has been most thoroughly characterized in the kidney.It is found in the basolateral and apical plasma membranes of the proximal tubules, the descending limb of the loop of Henle, and in the descending portion of the vasa...

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AQP2

Aquaporin 2

AQP2 is found in the apical cell membranes of the kidney's collecting duct principal cells and in intracellular vesicles located throughout the cell.-Regulation:It is the only aquaporin regulated by vasopressin....

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AQP3

Aquaporin 3

Aquaporin 3 is found in the basolateral cell membrane of principal collecting duct cells and provide a pathway for water to exit these cells. In kidney, AQP3 gene expression is not regulated by vasopressin . This protein is also a determinant for the GIL blood group system.-External links:* at...

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AQP4

Aquaporin 4

Aquaporin 4 also known as AQP4 is protein which in humans is encoded by the AQP4 gene. AQP4 belongs to the aquaporin family of integral membrane proteins that conduct water through the cell membrane.- Function :...

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AQP5

AQP5

Aquaporin-5 is a protein that in humans is encoded by the AQP5 gene.- External links :...

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AQP7

AQP7

Aquaporin-7 is a protein that in humans is encoded by the AQP7 gene.- External links :...

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AQP8

AQP8

Aquaporin-8 is a protein that in humans is encoded by the AQP8 gene.- External links :...

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AQP9

AQP9

Aquaporin-9 is a protein that in humans is encoded by the AQP9 gene.- External links :...

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MIP

MIP (gene)

Lens fiber major intrinsic protein is a protein that in humans is encoded by the MIP gene.-Further reading:...