Integral membrane protein


Integral membrane protein

An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes denaturing agents.

IMPs comprise a very significant fraction of the proteins encoded in the genome.

tructure

Three-dimensional structures of only ~160 different integral membrane proteins are currently determined at atomic resolution by X-ray crystallography or Nuclear magnetic resonance spectroscopy due to the difficulties with extraction and crystallization. In addition, structures of many water-soluble domains of IMPs are available in the Protein Data Bank. Their membrane-anchoring α-helices have been removed to facilitate the extraction and crystallization.

IMPs can be divided into two groups:
# Transmembrane proteins
# Integral monotopic proteins

Integral transmembrane protein

The most common type of IMP is the transmembrane protein (TM), which spans the entire biological membrane. Such a protein may cross the membrane only once or it may weave in and out, crossing several times. TM proteins can be categorized as Type I, which are positioned such that their amino-terminus is outside of the membrane, or Type II, which have their carboxy-terminus outside of the membrane.

Integral monotopic proteins

Integral monotopic proteins are permanently attached to the membrane from one side.

Three-dimensional structures of the following integral monotopic proteins have been determined:
*prostaglandin H2 syntheses 1 and 2 (cyclooxygenases) [http://opm.phar.umich.edu/families.php?superfamily=37] ,
*lanosterol synthase and squalene-hopene cyclase [http://opm.phar.umich.edu/families.php?superfamily=38] ,
*microsomal prostaglandin E synthase [http://opm.phar.umich.edu/protein.php?pdbid=1z9h] ,
*carnitine O-palmitoyltransferase 2 [http://opm.phar.umich.edu/families.php?superfamily=183] . There are also structures of integral monotopic "domains" of transmembrane proteins:
*monoamine oxidases A and B [http://opm.phar.umich.edu/families.php?family=176] ,
*fatty acid amide hydrolase [http://opm.phar.umich.edu/families.php?superfamily=58] ,
*mammalian cytochrome P450 oxidases [http://opm.phar.umich.edu/families.php?superfamily=41] ,
*corticosteroid 11-beta-dehydrogenases [http://opm.phar.umich.edu/families.php?superfamily=127] .Such domains require detergents for extraction or crystallization, even after removal of their transmembrane helices. Therefore, they are often classified as integral monotopic "proteins" [http://blanco.biomol.uci.edu/Membrane_Proteins_xtal.html]

Function

IMPs include transporters, channels, receptors, enzymes, structural membrane-anchoring domains, proteins involved in accumulation and transduction of energy, and proteins responsible for cell adhesion. Classification of transporters can be found in [http://www.tcdb.org/ TCDB database] .

References

*Booth, P.J., Templer, R.H., Meijberg, W., Allen, S.J., Curran, A.R., and Lorch, M. 2001. In vitro studies of membrane protein folding. "Crit. Rev. Biochem. Mol. Biol." 36: 501-603.
*Bracey M.H., Cravatt B.F., Stevens R.C., Cravatt B.F. 2004. Structural commonalities among integral membrane enzymes. "FEBS Lett." 567: 159-165.
*Bowie J.U. 2001. Stabilizing membrane proteins. "Curr. Op. Struct. Biol." 11: 397-402.
*Bowie J.U. 2005. Solving the membrane protein folding problem. "Nature" 438: 581-589.
*DeGrado W.F., Gratkowski H. and Lear J.D. 2003. How do helix-helix interactions help determine the folds of membrane proteins? Perspectives from the study of homo-oligomeric helical bundles. "Protein Sci." 12: 647-665.
*Popot J-L. and Engelman D.M. 2000. Helical membrane protein folding, stability, and evolution. "Annu. Rev. Biochem." 69: 881-922.
*"Protein-lipid interactions" (Ed. L.K. Tamm) Wiley, 2005.

ee also

*Membrane proteins
*Transmembrane proteins
*Peripheral membrane proteins

Examples

Examples of integral membrane proteins:
*Integrin
*Cadherin
*Insulin receptor
*NCAM
*Selectin
*Some types of cell adhesion proteins
*Some types of receptor proteins
*Glycophorin
*Rhodopsin
*Band 3
*CD36

External links

* [http://www.mpdb.ul.ie/ Membrane PDB] Database of 3D structures of integral membrane proteins and hydrophobic peptides with emphasis on crystallization conditions
* [http://blanco.biomol.uci.edu/Membrane_Proteins_xtal.html Membrane proteins of known 3D structure] from Stephen White laboratory
* [http://opm.phar.umich.edu/ Orientations of proteins in membranes database] Calculated spatial positions of transmembrane, integral monotopic, and peripheral proteins in membranes


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • integral membrane protein — A protein that is firmly anchored in a membrane (unlike a peripheral membrane protein). Most is known about the integral proteins of the plasma membrane, where important examples include hormone receptors, ion channels, and transport proteins. An …   Dictionary of molecular biology

  • integral membrane protein — see membrane p …   Medical dictionary

  • membrane protein — A protein with regions permanently attached to a membrane (peripheral membrane protein), or inserted into a membrane (integral membrane protein). Insertion into a membrane implies hydrophobic domains in the protein. All transport proteins are… …   Dictionary of molecular biology

  • Membrane protein — Crystal structure of Potassium channel KvAP. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue dots. A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an… …   Wikipedia

  • membrane protein — a protein found in association with the cell membrane, either attached to (peripheral or extrinsic) or inserted in (integral or intrinsic) the membrane; possible roles include enzyme, receptor for a hormone or other molecule, and mediator of… …   Medical dictionary

  • Peripheral membrane protein — Peripheral membrane proteins are proteins that adhere only temporarily to the biological membrane with which they are associated. These molecules attach to integral membrane proteins, or penetrate the peripheral regions of the lipid bilayer. The… …   Wikipedia

  • peripheral membrane protein — Membrane proteins that are bound to the surface of the membrane and not integrated into the hydrophobic region. Usually soluble and were originally thought to bind to integral proteins by ionic and other weak forces (and could therefore be… …   Dictionary of molecular biology

  • Outer membrane protein OpcA — Identifiers Symbol OpcA Pfam PF07239 …   Wikipedia

  • Protein (disambiguation) — Protein is a class of biomolecules composed of amino acid chains.Protein may also refer to:Biochemistry* Antifreeze protein, class of polypeptides produced by certain fish, vertebrates, plants, fungi and bacteria * Conjugated protein, protein… …   Wikipedia

  • Membrane topology — In biochemistry, the membrane topology of an transmembrane protein describes which portions of the amino acid sequence of the protein lie within the plane of the surrounding lipid bilayer and which portions protrude into the watery environment on …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.