Major intrinsic proteins

Major intrinsic proteins
Major intrinsic protein
PDB 1fx8 EBI.jpg
Structure of a glycerol-conducting channel.[1]
Symbol MIP
Pfam PF00230
InterPro IPR000425
SCOP 1fx8
TCDB 1.A.8
OPM family 7
OPM protein 1z98

Major intrinsic proteins are a large family of transmembrane protein channels that are grouped together on the basis of sequence similarities[2][3][4][5]. Proteins from this family exhibit essentially two distinct types of channel properties: (1) specific water transport by the aquaporins, and (2) small neutral solutes transport, such as glycerol by the glycerol facilitators.



MIP family includes the following channels:

  • Mammalian major intrinsic protein (MIP). MIP is the major component of lens fibre gap junctions.
  • Mammalian aquaporins[5]. 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.


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[6].

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


Human proteins containing this domain



  1. ^ Fu D, Libson A, Miercke LJ, et al. (October 2000). "Structure of a glycerol-conducting channel and the basis for its selectivity". Science 290 (5491): 481–6. doi:10.1126/science.290.5491.481. PMID 11039922. 
  2. ^ Reizer J, Reizer A, Saier Jr MH (1993). "The MIP family of integral membrane channel proteins: sequence comparisons, evolutionary relationships, reconstructed pathway of evolution, and proposed functional differentiation of the two repeated halves of the proteins". Crit. Rev. Biochem. Mol. Biol. 28 (3): 235–257. doi:10.3109/10409239309086796. PMID 8325040. 
  3. ^ Pao GM, Johnson KD, Chrispeels MJ, Sweet G, Sandal NN, Wu LF, Saier Jr MH, Hofte H (1991). "Evolution of the MIP family of integral membrane transport proteins". Mol. Microbiol. 5 (1): 33–37. doi:10.1111/j.1365-2958.1991.tb01823.x. PMID 2014003. 
  4. ^ Wistow GJ, Pisano MM, Chepelinsky AB (1991). "Tandem sequence repeats in transmembrane channel proteins". Trends Biochem. Sci. 16 (5): 170–171. doi:10.1016/0968-0004(91)90065-4. PMID 1715617. 
  5. ^ a b Chrispeels MJ, Agre P (1994). "Aquaporins: water channel proteins of plant and animal cells". Trends Biochem. Sci. 19 (10): 421–425. doi:10.1016/0968-0004(94)90091-4. PMID 7529436. 
  6. ^ . pp. -. 
  7. ^ Reid ME, Lomas-francis C (2002). "Molecular approaches to blood group identification". Curr Opin Hematol 9 (2): 152–159. doi:10.1097/00062752-200203000-00012. PMID 11845000.