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Encyclopedia > Transmembrane receptor

Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cell's plasma membrane, but also in the membranes of some subcellular compartments and organelles. Binding to a signalling molecule or sometimes to a pair of such molecules on one side of the membrane, transmembrane receptors initiate a response on the other side. In this way they play a unique and important role in cellular communications and signal transduction. Integral membrane protein of the transmembrane type An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that in most cases spans the biological membrane with which it is associated (especially the plasma membrane) or which, in any case, is sufficiently embedded in the membrane to remain... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... A biological membrane or biomembrane is a membrane which acts as a barrier within or around a cell. ... Schematic of typical animal cell, showing subcellular components. ... It has been suggested that cell signaling be merged into this article or section. ...


Many transmembrane receptors are composed of two or more protein subunits which operate collectively and may dissociate when ligands bind, fall off, or at another stage of their "activation" cycles. They are often classified based on their molecular structure, or because the structure is unknown in any detail for all but a few receptors, based on their hypothesized (and sometimes experimentally verified) membrane topology. The polypeptide chains of the simplest are predicted to cross the lipid bilayer only once, while others cross as many as seven times (the so-called G-protein coupled receptors). In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ... It has been suggested that this article or section be merged with ligand. ... In biochemistry, the tertiary structure of a protein is its overall shape. ... 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 either side. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A diagonal molecular slab from the DPPC lipid bilayer simulation1; color scheme: PO4 - green, N(CH3)3 - violet, water - blue, terminal CH3 - yellow, O - red, glycol C - brown, chain C - grey. ... The seven transmembrane α-helix structure of a G protein-coupled receptor. ...


Like any integral membrane protein, a transmembrane receptor may be subdivided into three parts or domains.


image:transmembrane_receptor.png
E=extracellular space; I=intracellular space; P=plasma membrane from meta; yet another one of my own drawings;-) File links The following pages link to this file: Transmembrane receptor Receptor (biochemistry) Categories: GFDL images ...

Contents


The extracellular domain

The extracellular domain is the part of the receptor that sticks out of the membrane on the outside of the cell or organelle. If the polypeptide chain of the receptor crosses the bilayer several times, the external domain can comprise several "loops" sticking out of the membrane. By definition, a receptor's main function is to recognize and respond to a specific ligand, for example, a neurotransmitter or hormone (although certain receptors respond also to changes in transmembrane potential), and in many receptors these ligands bind to the extracellular domain. Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... In membrane biophysics sometimes used interchangeably with cell potential, but applicable to any lipid bilayer or membrane. ...


The transmembrane domain

In the majority of receptors for which structural evidence exists, transmembrane alpha helices make up most of the transmembrane domain. In certain receptors, such as the nicotinic acetylcholine receptor, the transmembrane domain forms a protein-lined pore through the membrane, or ion channel. Upon activation of an extracellular domain by binding of the appropriate ligand, the pore becomes accessible to ions, which then pass through. In other receptors, the transmembrane domains are presumed to undergo a conformational change upon binding, which exerts an effect intracellularly. In some receptors, such as members of the 7TM superfamily, the transmembrane domain may contain the ligand binding pocket (evidence for this and for much of what else is known about this class of receptors is based in part on studies of bacteriorhodopsin, the detailed structure of which has been determined by crystallography). Within an integral membrane protein, a transmembrane helix is a segment that is alpha-helical in structure, roughly 20 amino acids in length and (though it may be presumed to lie within the protein, out of contact with the surrounding lipid bilayer) is said to span the membrane. ... An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of the neurotransmitter acetylcholine. ... A pore, in general, is some form of opening, usually very small. ... Another, unrelated ion channeling process is part of ion implantation. ... Bold textLink titleLink title Bacteriorhodopsin is the photosynthetic pigment used by archaea, most notably halobacteria. ...


The intracellular domain

The intracellular (or cytoplasmic) domain of the receptor interacts with the interior of the cell or organelle, relaying the signal. There are two fundamentally different ways for this interaction: Cytoplasm is like jelly-like material that fills cells. ...

  • The intracellular domain communicates via specific protein-protein-interactions with effector proteins, which in turn send the signal along a signal chain to its destination.
  • The intracellular domain has enzymatic activity. Often, this is a tyrosine kinase activity. The enzymatic activity can also be located on an enzyme associated with the intracellular domain.

Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... Tyrosine kinases are a subclass of protein kinase, see there for the principles of protein phosphorylation A tyrosine kinase (EC 2. ...

Regulation of receptor activity

There are several ways for the cell to regulate the activity of a transmembrane receptor. Most of them work through the intracellular domain. The most important ways are phosphorylation and internalization (see ubiquitin). Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule. ... To internalize is to put something inside of borders where it did not originally belong. ... // Background Ubiquitylation, also termed ubiquitination, refers to the process particular to eukaryotes whereby a protein is post-translationally modified by covalent attachment of a small protein. ...


See also


  Results from FactBites:
 
Opioid Receptors (5011 words)
receptor was accepted as a member of the "family" of opioid receptors on the basis of its structural homology towards the classical types, there is no corresponding pharmacological homology.
The opioid receptor family, in common with the somatostatin receptor family, is somewhat unusual in that all of the cloned opioid receptor types belong to the G
Among the receptors for the many neuropeptides that exist in the nervous system, the opioid receptors are unique in that there existed before the discovery of the natural agonists, an abundance of non-peptide ligands with which the pharmacology of the receptors was already defined.
Transmembrane receptor: Definition and Links by Encyclopedian.com (556 words)
Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cell's plasma membrane, but also in the membranes of some subcellular compartments and organelles.
a receptor's main function is to recognize and respond to a specific ligand, for example, a neurotransmitter or hormone (although certain receptors respond also to changes in transmembrane potential), and in many receptors these ligands bind to the extracellular domain.
In some receptors, such as members of the 7TM superfamily, the transmembrane domain may contain the ligand binding pocket (evidence for this and for much of what else is known about this class of receptors is based in part on studies of bacteriorhodopsin[?], the detailed structure of which has been determined by crystallography).
  More results at FactBites »

 
 

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