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Membrane protein
 
 
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Also see transmembrane protein
Transmembrane protein

A transmembrane protein is a protein that spans the entire biological membrane. Transmembrane proteins aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them can be also extracted using denaturing agents....
.
A membrane protein is a protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 molecule that is attached to, or associated with the membrane of a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 or an organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
. More than half of all proteins interact with membranes. Membrane proteins can be classified into two groups, based on the strength of their association with the membrane.

Main categories
Integral membrane protein
Integral membrane protein

An Integral Membrane Protein is a protein molecule that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes Denaturation agents....
s are permanently attached to the membrane.






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Also see transmembrane protein
Transmembrane protein

A transmembrane protein is a protein that spans the entire biological membrane. Transmembrane proteins aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them can be also extracted using denaturing agents....
.
A membrane protein is a protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 molecule that is attached to, or associated with the membrane of a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 or an organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
. More than half of all proteins interact with membranes. Membrane proteins can be classified into two groups, based on the strength of their association with the membrane.

Main categories


Integral membrane protein
Integral membrane protein

An Integral Membrane Protein is a protein molecule that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes Denaturation agents....
s are permanently attached to the membrane. They can be defined as those proteins which require a detergent
Detergent

A detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning....
 (such as SDS
Sodium dodecyl sulfate

Sodium lauryl sulfate or sodium dodecyl sulfate is an anionic surfactant that is used in industrial products including engine degreasers, floor cleaners, and car wash soaps; as well as in household products such as toothpastes, shampoos, shaving foams, some dissolvable aspirins, fiber therapy caplets, and bubble baths for its thicken...
 or Triton X-100) or some other apolar solvent to be displaced. They can be classified according to their relationship with the bilayer:
  • Transmembrane proteins span the entire membrane. The transmembrane regions of the proteins are either beta-barrels or alpha-helical
    Alpha helix

    A common motif in the secondary structure of proteins, the alpha helix is a right- or left-handed coiled conformation, resembling a spring , in which every backbone amino group donates a hydrogen bond to the backbone carbonyl group of the amino acid four residues earlier ....
    . The alpha-helical domains are present in all types of biological membranes including outer membrane
    Outer membrane

    The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane include a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's peptidoglycan by Braun's lipoprotein....
    s. The beta-barrels were found only in outer membrane
    Outer membrane

    The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane include a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's peptidoglycan by Braun's lipoprotein....
    s of Gram-negative bacteria, lipid-rich cell walls of a few Gram-positive bacteria, and outer membrane
    Outer membrane

    The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane include a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's peptidoglycan by Braun's lipoprotein....
    s of mitochondria and chloroplasts.


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


Peripheral membrane protein
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....
s are temporarily attached either to the lipid bilayer
Lipid bilayer

A lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cell ....
 or to integral proteins by a combination of hydrophobic, electrostatic, and other non-covalent interactions. Peripheral proteins dissociate following treatment with a polar reagent, such as a solution with an elevated pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 or high salt concentrations.

Integral and peripheral proteins may be post-translationally modified, with added fatty acid
Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail , which is either saturation or Unsaturated compound....
 or prenyl chains, or GPI
GPI

GPI may refer to:* Global Protection & Intelligence, Inc. Private Public Figure, Executive, Diplomatic protective service based in Los Angeles, California USA....
 (glycosylphosphatidylinositol), which may be anchored in the lipid bilayer.

Classification of membrane proteins to integral and peripheral does not include some polypeptide toxins, such as colicin
Colicin

A colicin is a type of bacteriocin produced by and toxic to some strains of Escherichia coli. Colicins are composed of three globular protein structural domains....
 A or alpha-hemolysin, and certain proteins involved in apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
. These proteins are water-soluble but can aggregate and associate irreversibly with the lipid bilayer and form alpha-helical or beta-barrel transmembrane channels. An alternative classification is to divide all membrane proteins to integral and amphitropic. The amphitropic are proteins that can exist in two alternative states: a water-soluble and a lipid bilayer-bound, whereas integral proteins can be found only in the membrane-bound state. The amphitropic protein category includes water-soluble channel-forming polypeptide toxins, which associate irreversibly with membranes, but excludes peripheral proteins that interact with other membrane proteins rather than with lipid bilayer.

Further reading

  • Protein-lipid interactions (Ed. L.K. Tamm) Wiley, 2005.
  • Popot J-L. and Engelman D.M. 2000. Helical membrane protein folding, stability, and evolution. Annu. Rev. Biochem. 69: 881-922.
  • Bowie J.U. 2005. Solving the membrane protein folding problem. Nature 438: 581-589.
  • Cho, W. and Stahelin, R.V. 2005. Membrane-protein interactions in cell signaling and membrane trafficking. Annu. Rev. Biophys. Biomol. Struct. 34: 119–151.
  • Goni F.M. 2002. Non-permanent proteins in membranes: when proteins come as visitors. Mol. Membr. Biol. 19: 237-245.
  • Johnson J.E. and Cornell R.B. 1999. Amphitropic proteins: regulation by reversible membrane interactions. Mol. Membr. Biol. 16: 217-235.
  • Seaton B.A. and Roberts M.F. Peripheral membrane proteins. pp. 355-403. In Biological Membranes (Eds. K. Mertz and B.Roux), Birkhauser Boston, 1996.
  • Dürr U.H.N., Waskell L., and Ramamoorthy A. The cytochromes P450 and b5 and their reductases-Promising targets for structural studies by advanced solid-state NMR spectroscopy, 2007. BBA Biomembranes 1768: 3235-3259.


See also

  • Integral membrane protein
    Integral membrane protein

    An Integral Membrane Protein is a protein molecule that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes Denaturation agents....
    s
  • Transmembrane protein
    Transmembrane protein

    A transmembrane protein is a protein that spans the entire biological membrane. Transmembrane proteins aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them can be also extracted using denaturing agents....
    s
  • Peripheral membrane protein
    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....
    s
  • Ion pump (biology)
    Ion pump (biology)

    In biology, an ion transporter, also called an ion pump, is a transmembrane protein that moves ions across a plasma membrane against their concentration gradient, in contrast to ion channels, where ions go through passive transport...
  • Carrier protein
    Carrier protein

    Carrier proteins are proteins that transport a specific substance or group of substances through intracellular compartments or in extracellular fluids or else across the cell membrane....
  • Ion channel
    Ion channel

    Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cell s by allowing the flow of ions down their electrochemical gradient....
  • Receptor (biochemistry)
    Receptor (biochemistry)

    In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
     (including G protein-coupled receptor
    G protein-coupled receptor

    G protein-coupled receptors , also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the Cell and activate inside signal transductio...
    )
  • Wikipedia:MeSH_D12.776#MeSH_D12.776.543_---_membrane_proteins


External links

  • from Stephen White laboratory
  • 3D structures of integral and amphitropic membrane proteins