Receptor (biochemistry)

Receptor (biochemistry)

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In biochemistry
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

, a receptor is a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 found on the surface of a cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

, which receives specific chemical signals from neighbouring cells or the wider environment within an organism. These signals tell a cell to do something—for example to divide or die, or to allow certain molecules to enter or exit the cell.

Receptors are protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 molecules, embedded in either the plasma membrane (cell surface receptors) or the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 (nuclear receptor
Nuclear receptor
In the field of molecular biology, nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones and certain other molecules...

s) of a cell, to which one or more specific kinds of signaling
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

 molecules may attach. A molecule which binds (attaches) to a receptor is called a ligand
Ligand (biochemistry)
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...

, and may be a peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...

 (short protein) or other small molecule, such as a neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

, a hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

, a pharmaceutical drug, or a toxin. Each kind of receptor can bind only certain ligand shapes. Each cell typically has many receptors, of many different kinds. Simply put, a receptor functions as a keyhole that opens a biochemical pathway when the proper ligand is inserted.

Ligand binding stabilizes a certain receptor conformation
Conformational change
A macromolecule is usually flexible and dynamic. It can change its shape in response to changes in its environment or other factors; each possible shape is called a conformation, and a transition between them is called a conformational change...

 (the three-dimensional shape of the receptor protein, with no change in sequence). This is often associated with gain of or loss of protein activity, ordinarily leading to some sort of cellular response. However, some ligands (e.g. antagonists
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

) merely block receptors without inducing any response. Ligand-induced changes in receptors result in cellular changes which constitute the biological activity of the ligands. Many functions of the human body are regulated by these receptors responding uniquely to specific molecules like this.

Structure


The shapes and actions of receptors are studied by X-ray crystallography
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...

, dual polarisation interferometry
Dual Polarisation Interferometry
Dual polarization interferometry is an analytical technique that can probe molecular scale layers adsorbed to the surface of a waveguide by using the evanescent wave of a laser beam confined to the waveguide...

, computer modelling
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

, and structure-function studies, which have advanced the understanding of drug action
Drug action
The action of drugs on the human body is called pharmacodynamics, and what the body does with the drug is called pharmacokinetics. The drugs that enter the human tend to stimulate certain receptors, ion channels, act on enzymes or transporter proteins...

 at the binding sites of receptors. Structure activity relationships correlate induced conformational changes with biomolecular activity, and are studied using dynamic techniques such as circular dichroism
Circular dichroism
Circular dichroism refers to the differential absorption of left and right circularly polarized light. This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel, and Aimé Cotton in the first half of the 19th century. It is exhibited in the absorption bands of optically active chiral...

 and dual polarisation interferometry
Dual Polarisation Interferometry
Dual polarization interferometry is an analytical technique that can probe molecular scale layers adsorbed to the surface of a waveguide by using the evanescent wave of a laser beam confined to the waveguide...

.

Depending on their functions and ligands
Ligand (biochemistry)
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...

, several types of receptors may be identified:
  • Some receptor proteins are 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. The regulatory protein subunits of many ion channels and...

    s.
  • Many hormone
    Hormone receptor
    A hormone receptor is a receptor protein on the surface of a cell or in its interior that binds to a specific hormone. The hormone causes many changes to take place in the cell....

     and neurotransmitter receptor
    Neurotransmitter receptor
    A Neurotransmitter receptor is a membrane receptor protein that is activated by a Neurotransmitter. A membrane protein interacts with the lipid bilayer that encloses the cell and a membrane receptor protein interacts with a chemical in the cells external environment, which binds to the cell...

    s are transmembrane proteins: transmembrane receptors are embedded in the phospholipid bilayer of cell membrane
    Cell membrane
    The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

    s, that allow the activation of signal transduction
    Signal transduction
    Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

     pathways in response to the activation by the binding molecule, or ligand
    Ligand (biochemistry)
    In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...

    .
    • Metabotropic receptor
      Metabotropic receptor
      Metabotropic receptor is a subtype of membrane receptors at the surface or in vesicles of eukaryotic cells.In the nervous system, based on their structural and functional characteristics, neurotransmitter receptors can be classified into two broad categories: metabotropic and ionotropic receptors...

      s are coupled to G protein
      G protein
      G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...

      s and affect the cell indirectly through enzyme
      Enzyme
      Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

      s which control ion channel
      Ion channel
      Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

      s.
    • Ionotropic receptors (also known as ligand-gated ion channel
      Ligand-gated ion channel
      Ligand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...

      s) contain a central pore which opens in response to the binding of ligand.
  • Another major class of receptors are intracellular
    Intracellular
    Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

     proteins such as those for steroid
    Steroid
    A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...

     and intracrine
    Intracrine
    Intracrine refers to a hormone that acts inside a cell. Steroid hormones act through intracellular receptors and, thus, may be considered to be intracrines. In contrast, peptide or protein hormones, in general, act as endocrines, autocrines, or paracrines by binding to their receptors present on...

     peptide hormone
    Peptide hormone
    Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...

     receptors. These receptors often can enter the cell nucleus
    Cell nucleus
    In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

     and modulate gene expression
    Gene expression
    Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

     in response to the activation by the ligand.


Membrane receptors are isolated from cell membranes by complex extraction procedures using solvents
Liquid-liquid extraction
Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid...

, detergents, and/or affinity purification.

Binding and activation


Ligand binding is an equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

 process. Ligands bind to receptors and dissociate from them according to the law of mass action.
(the brackets stand for concentrations)


One measure of how well a molecule fits a receptor is the binding affinity, which is inversely related to the dissociation constant
Dissociation constant
In chemistry, biochemistry, and pharmacology, a dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into...

 Kd. A good fit corresponds with high affinity and low Kd. The final biological response (e.g. second messenger cascade
Second messenger system
Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus. They relay the signals of hormones like epinephrine , growth factors, and others, and cause some kind of change in the activity of the cell...

, muscle contraction), is only achieved after a significant number of receptors are activated.

The receptor-ligand affinity is greater than enzyme-substrate affinity. Whilst both interactions are specific and reversible, there is no chemical modification of the ligand as seen with the substrate upon binding to its enzyme.

If the receptor exists in two states (see this picture), then the ligand binding must account for these two receptor states. For a more detailed discussion of two-state binding, which is thought to occur as an activation mechanism in many receptors see this link.

Constitutive activity


A receptor which is capable of producing its biological response in the absence of a bound ligand is said to display "constitutive activity". The constitutive activity of receptors may be blocked by inverse agonist
Inverse agonist
In the field of pharmacology, an inverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist....

 binding. Mutations in receptors that result in increased constitutive activity underlie some inherited diseases, such as precocious puberty (due to mutations in luteinizing hormone receptors) and hyperthyroidism (due to mutations in thyroid-stimulating hormone receptors). For the use of statistical mechanics
Statistical mechanics
Statistical mechanics or statistical thermodynamicsThe terms statistical mechanics and statistical thermodynamics are used interchangeably...

 in a quantitative study of the
ligand-receptor binding affinity, see the comprehensive article on the configuration integral.

Theories of drug receptor interaction


Occupation theory

Drug effect is directly proportional to number of receptors occupied.
Drug effect ceases as drug-receptor complex dissociate

Ariens & Stephenson theory

introduced Terms of "affinity" & "efficacy"
Affinity: ability of the drug to combine with receptor to create drug-receptor complex
Efficacy: ability of the drug-receptor complex to initiate a response

Affinity “drug-receptor interaction” is governed by the law of mass action.

In this theory

Agonist: drug with high affinity & high intrinsic activity
Partial agonist: drug with high affinity & low intrinsic activity
Antagonist: drug with high affinity & low intrinsic activity

Rate theory

The activation of receptors is directly proportional to the total number of encounters of the drug with its receptors per unit time
Pharmacological activity is directly proportional to the rate of dissociation & association not number of receptors occupied

Agonist:drug with fast association & fast dissociation
Partial agonist:drug with intermediate association & intermediate dissociation
Antagonist:drug with fast association & slow dissociation

Induced fit theory

As the drug approaches the receptor the receptor alters the conformation of its binding site to produce drug—receptor complex

Agonists versus antagonists


Not every ligand that binds to a receptor also activates the receptor. The following classes of ligands exist:
  • (Full) agonist
    Agonist
    An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

    s
    are able to activate the receptor and result in a maximal biological response. Most natural ligands are full agonists.
  • Partial agonists do not activate receptors thoroughly, causing responses which are partial compared to those of full agonists.
  • Antagonists
    Receptor antagonist
    A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

     bind to receptors but do not activate them. This results in receptor blockage, inhibiting the binding of other agonists.
  • Inverse agonists reduce the activity of receptors by inhibiting their constitutive activity.

Peripheral membrane protein receptors



These receptors are relatively rare compared to the much more common types of receptors that cross the cell membrane. An example of a receptor that is a peripheral membrane protein is the elastin receptor
GLB1
Galactosidase, beta 1, also known as GLB1, is a protein which in humans is encoded by the GLB1 gene.The GLB1 protein is a beta-galactosidase that cleaves the terminal beta-galactose from ganglioside substrates and other glycoconjugates...

.

G protein-coupled receptors



These receptors are also known as seven transmembrane receptors or 7TM receptors, because they pass through the membrane seven times.
  • Muscarinic acetylcholine receptor
    Muscarinic acetylcholine receptor
    Muscarinic receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled in the plasma membranes of certain neurons and other cells...

     (Acetylcholine
    Acetylcholine
    The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

     and Muscarine
    Muscarine
    Muscarine, L--muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. Mushrooms in the genera Entoloma and Mycena have also been found to contain levels of muscarine which can be dangerous if ingested...

    )
  • Adenosine receptor
    Adenosine receptor
    The adenosine receptors are a class of purinergic receptors, G protein-coupled receptors with adenosine as endogenous ligand.-Pharmacology:...

    s (Adenosine)
  • Adrenoceptors (also known as Adrenergic receptor
    Adrenergic receptor
    The adrenergic receptors are a class of metabotropic G protein-coupled receptors that are targets of the catecholamines, especially noradrenaline and adrenaline ....

    s, for adrenaline, and other structurally related hormone
    Hormone
    A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

    s and drugs
    Medication
    A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...

    )
  • GABA receptor
    GABA receptor
    The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid , the chief inhibitory neurotransmitter in the vertebrate central nervous system...

    s, Type-B (γ-Aminobutyric acid
    Gamma-aminobutyric acid
    γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...

     or GABA)
  • Angiotensin receptor
    Angiotensin receptor
    The angiotensin receptors are a class of G protein-coupled receptors with angiotensin II as their ligands. They are important in the renin-angiotensin system: they are responsible for the signal transduction of the vasoconstricting stimulus of the main effector hormone, angiotensin...

    s (Angiotensin
    Angiotensin
    Angiotensin, a peptide hormone, causes blood vessels to constrict, and drives blood pressure up. It is part of the renin-angiotensin system, which is a major target for drugs that lower blood pressure. Angiotensin also stimulates the release of aldosterone, another hormone, from the adrenal cortex...

    )
  • Cannabinoid receptor
    Cannabinoid receptor
    The cannabinoid receptors are a class of cell membrane receptors under the G protein-coupled receptor superfamily. As is typical of G protein-coupled receptors, the cannabinoid receptors contain seven transmembrane spanning domains...

    s (Cannabinoids
    Cannabinoids
    Cannabinoids are a class of chemical compounds that include the phytocannabinoids , and chemical compounds that mimic the actions of phytocannabinoids or have a similar structure...

    )
  • Cholecystokinin receptor
    Cholecystokinin receptor
    Cholecystokinin receptors or CCK receptors are a group of G-protein coupled receptors which bind the peptide hormones cholecystokinin or gastrin...

    s (Cholecystokinin
    Cholecystokinin
    Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...

    )
  • Dopamine receptor
    Dopamine receptor
    Dopamine receptors are a class of metabotropic G protein-coupled receptors that are prominent in the vertebrate central nervous system . The neurotransmitter dopamine is the primary endogenous ligand for dopamine receptors....

    s (Dopamine
    Dopamine
    Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

    )
  • Glucagon receptor
    Glucagon receptor
    The glucagon receptor is a 62 kDa protein that is activated by glucagon and is a member of the class B G-protein coupled family of receptors, coupled to G alpha i, Gs and to a lesser extent G alpha q. Stimulation of the receptor results in activation of adenylate cyclase and increased levels of...

    s (Glucagon
    Glucagon
    Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...

    )
  • Melatonin receptor
    Melatonin receptor
    A melatonin receptor is a G protein-coupled receptor which binds melatonin.Three types of melatonin receptor have been cloned. The MT1 and MT2 receptor subtypes are present in humans and other mammals, while an additional melatonin receptor subtype MT3 has been identified in amphibia and...

    s (Melatonin
    Melatonin
    Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...

    )
  • Metabotropic glutamate receptor
    Metabotropic glutamate receptor
    The metabotropic glutamate receptors, or mGluRs, are a type of glutamate receptor that are active through an indirect metabotropic process. They are members of the group C family of G-protein-coupled receptors, or GPCRs...

    s (Glutamate)
  • Histamine receptor
    Histamine receptor
    The histamine receptors are a class of G protein-coupled receptors with histamine as their endogenous ligand.There are four known histamine receptors:*H1 receptor*H2 receptor*H3 receptor*H4 receptor-Comparison:...

    s (Histamine
    Histamine
    Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...

    )
  • Olfactory receptor
    Olfactory receptor
    Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain...

    s (for the sense of smell
    Olfaction
    Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

    )
  • Opioid receptor
    Opioid receptor
    Opioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors...

    s (Opioid
    Opioid
    An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

    s)
  • Protease-activated receptor
    Protease-activated receptor
    Protease-activated receptors are a subfamily of related G protein-coupled receptors that are activated by cleavage of part of their extracellular domain. They are highly expressed in platelets, but also on endothelial cells, myocytes and neurons....

    s
  • Rhodopsin
    Rhodopsin
    Rhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light,...

     (a photoreceptor protein
    Photoreceptor protein
    Photoreceptors are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria...

    )
  • Secretin receptor
    Secretin receptor
    Human secretin receptor is a G protein-coupled receptor which binds secretin and is the leading member of the class B GPCR subfamily.-Interactions:...

    s (Secretin
    Secretin
    Secretin is a hormone that controls the secretions into the duodenum, and also separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn...

    )
  • Serotonin receptors, except Type-3 (Serotonin
    Serotonin
    Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

    , also known as 5-Hydroxytryptamine or 5-HT)
  • Somatostatin receptor
    Somatostatin receptor
    There are five known somatostatin receptors:* SST1 * SST2 * SST3 * SST4 * SST5 All are G protein-coupled seven transmembrane receptors.-External links:...

    s (Somatostatin
    Somatostatin
    Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...

    )
  • Trace-amine associated receptors (Trace amines)
  • Calcium-sensing receptor
    Calcium-sensing receptor
    The calcium-sensing receptor is a Class C G-protein coupled receptor which senses extracellular levels of calcium ion. In the parathyroid gland, the calcium-sensing receptor controls calcium homeostasis by regulating the release of parathyroid hormone .-Signal transduction:The release of PTH is...

     (Calcium
    Calcium
    Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

    )
  • Chemokine receptors (Chemokines)

many more ...

Receptor tyrosine kinases



These receptors detect ligands and propagate signals via the tyrosine kinase
Tyrosine kinase
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell. It functions as an "on" or "off" switch in many cellular functions....

 of their intracellular domains.
This family of receptors includes;
  • Erythropoietin receptor
    Erythropoietin receptor
    The erythropoietin receptor is a protein that in humans is encoded by the EPOR gene. EpoR is a 59 kDa peptide and is a member of the cytokine receptor family. EpoR pre-exists as dimers...

     (Erythropoietin
    Erythropoietin
    Erythropoietin, or its alternatives erythropoetin or erthropoyetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production...

    )
  • Insulin receptor
    Insulin receptor
    In molecular biology, the insulin receptor is a transmembrane receptor that is activated by insulin. It belongs to the large class of tyrosine kinase receptors....

     (Insulin
    Insulin
    Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

    )
  • Eph receptor
    Eph receptor
    Eph receptors are components of cell signalling pathways involved in animal growth and development, forming the largest sub-family of receptor tyrosine kinases . The extracellular domain of an Eph receptor interacts with ephrin ligands, which may be tethered to neighbouring cells...

    s
  • Insulin-like growth factor 1 receptor
  • various other growth factor
    Growth factor receptor
    A growth factor receptor is a receptor which binds to growth factor.These receptors may use the JAK/STAT, MAP kinase, and PI3 kinase pathways....

     and cytokine receptor
    Cytokine receptor
    Cytokine receptors are receptors that bind cytokines.In recent years, the cytokine receptors have come to demand the attention of more investigators than cytokines themselves, partly because of their remarkable characteristics, and partly because a deficiency of cytokine receptors has now been...

    s
  • ....

Guanylyl cyclase receptors

  • GC-A & GC-B: receptors for Atrial-natriuretic peptide (ANP) and other natriuretic peptides
  • GC-C: Guanylin
    Guanylin
    Guanylin is a 15 amino acid polypeptide that is secreted by goblet cells in the colon. Guanylin acts as an agonist of the guanylyl cyclase receptor GC-C and regulates electrolyte and water transport in intestinal and renal epithelia...

     receptor

Ionotropic receptors



Ionotropic receptors are heteromeric or homomeric
Homomeric
A homomeric substance is one which is made out of any number of identical products or molecules.e.g. A homomeric peptide = glutathione A peptide which is made up of only a single type of amino acid subunit; e.g., alanylalanylalanine.ALA-ALA-ALA...

 oligomers. They are receptors that respond to extracellular ligands and receptors that respond to intracellular ligands.

Extracellular ligands

Receptor Ligand Ion current
Nicotinic acetylcholine receptor
Nicotinic acetylcholine receptor
Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...

 
Acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

, Nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...

 
Na+, K+, Ca2+
Glycine receptor
Glycine receptor
The glycine receptor, or GlyR, is the receptor for the amino acid neurotransmitter glycine. GlyR is an ionotropic receptor that produces its effects through chloride current...

 (GlyR)
Glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

, Strychnine
Strychnine
Strychnine is a highly toxic , colorless crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine causes muscular convulsions and eventually death through asphyxia or sheer exhaustion...

 
Cl > HCO3
GABA receptor
GABA receptor
The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid , the chief inhibitory neurotransmitter in the vertebrate central nervous system...

s: GABA-A, GABA-C
GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...

 
Cl > HCO3
Glutamate receptor
Glutamate receptor
Glutamate receptors are synaptic receptors located primarily on the membranes of neuronal cells. Glutamate is one of the 20 amino acids used to assemble proteins and as a result is abundant in many areas of the body, but it also functions as a neurotransmitter and is particularly abundant in the...

s: NMDA receptor
NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....

, AMPA receptor
AMPA receptor
The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor is a non-NMDA-type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system . Its name is derived from its ability to be activated by the artificial glutamate analog AMPA...

, and Kainate receptor
Kainate receptor
Kainate receptors, or KARs, are non-NMDA ionotropic receptors which respond to the neurotransmitter glutamate. They were first identified as a distinct receptor type through their selective activation by the agonist kainate, a drug first isolated from red algae Digenea simplex. KARs are less well...

 
Glutamate  Na+, K+, Ca2+
5-HT3 receptor  Serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

 
Na+, K+
P2X receptors  ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 
Ca2+, Na+, Mg2+

Intracellular ligands

Receptor Ligand Ion current
cyclic nucleotide-gated ion channel
Cyclic nucleotide-gated ion channel
Cyclic nucleotide-gated ion channels are ion channels that function in response to the binding of cyclic nucleotides. CNG channels are nonselective cation channels that are found in the membranes of various types of cells.- Discovery :...

s
cGMP
Cyclic guanosine monophosphate
Cyclic guanosine monophosphate is a cyclic nucleotide derived from guanosine triphosphate . cGMP acts as a second messenger much like cyclic AMP...

 (vision
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...

), cAMP
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...

 and cGTP (olfaction)
Na+, K+
IP3 receptor
Inositol triphosphate receptor
Inositol trisphosphate receptor is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol trisphosphate . InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis,...

 
IP3
Inositol triphosphate
Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell...

 
Ca2+
Intracellular ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 receptors
ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 (closes channel)
K+
Ryanodine receptor
Ryanodine receptor
Ryanodine receptors form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons...

 
Ca2+ Ca2+


The entire repertoire of human plasma membrane receptors is listed at the Human Plasma Membrane Receptome (http://www.receptome.org).

Various

  • Ionotropic receptors (IP3 receptor
    Inositol triphosphate receptor
    Inositol trisphosphate receptor is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol trisphosphate . InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis,...

     above)
  • sigma1
    Sigma-1 receptor
    The sigma-1 receptor is a chaperone protein at the endoplasmatic reticulum that modulates calcium signaling through the IP3 receptor. In humans, the sigma-1 receptor is encoded by the SIGMAR1 gene....

     (neurosteroids
    Neuroactive steroid
    Neuroactive steroids rapidly alter neuronal excitability through interaction with neurotransmitter-gated ion channels. In addition, these steroids may also exert effects on gene expression via intracellular steroid hormone receptors...

    )
  • G protein-coupled receptors

Role in genetic disorders


Many genetic disorder
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....

s involve hereditary defects in receptor genes. Often, it is hard to determine whether the receptor is nonfunctional or the hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 is produced at decreased level; this gives rise to the "pseudo-hypo-" group of endocrine disorders
Endocrinology
Endocrinology is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions called hormones, the integration of developmental events such as proliferation, growth, and differentiation and the coordination of...

, where there appears to be a decreased hormonal level while in fact it is the receptor that is not responding sufficiently to the hormone.

Receptor regulation


Cells can increase (upregulate) or decrease (downregulate) the number of receptors to a given hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 or neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

 to alter its sensitivity to this molecule. This is a locally acting feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...

 mechanism.

Receptor desensitization
  • Uncoupling of receptor effector molecules.
  • Receptor sequestration
    Endocytosis
    Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...

     (internalization).

In immune system



The main receptors in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 are pattern recognition receptors (PRRs), toll-like receptor
Toll-like receptor
Toll-like receptors are a class of proteins that play a key role in the innate immune system. They are single, membrane-spanning, non-catalytic receptors that recognize structurally conserved molecules derived from microbes...

s (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptor
Complement receptor
A complement receptor is a receptor of the complement system, a part of the mediated innate immune system. Complement receptors are responsible for detecting pathogens by mechanisms not mediated by antibodies. Complement activity is not antigen sensitive, but can be triggered by specific antigens...

s, Fc receptors, B cell receptors and T cell receptor
T cell receptor
The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is responsible for recognizing antigens bound to major histocompatibility complex molecules...

s.

See also

  • Ki Database
    Ki Database
    The Ki Database is a public domain database of published binding affinities of drugs and chemical compounds for receptors, neurotransmitter transporters, ion channels, and enzymes...

  • Ion channel linked receptors
    Ion channel linked receptors
    Ion channel linked receptors are cell membrane bound receptors. They act through synaptic signaling on electrically excitable cells. The ion channels opening and closing is controlled by neurotransmitters....

  • Neuropsychopharmacology
    Neuropsychopharmacology
    Neuropsychopharmacology is an interdisciplinary science related to psychopharmacology and fundamental neuroscience...

  • Schild regression
    Schild regression
    Schild regression analysis, named for Heinz Otto Schild, is a useful tool for studying the effects of agonists and antagonists on the cellular response caused by the receptor or on ligand-receptor binding....

     for ligand receptor inhibition
  • Signal transduction
    Signal transduction
    Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

  • Stem cell marker
    Stem cell marker
    Stem cell markers are genes and their protein products used by scientists to isolate and identify stem cells. Stem cells can also be identified by functional assays. Below is a list of genes/protein products that can be used to identify various types of stem cells, or functional assays that do the...

  • Wikipedia:MeSH D12.776#MeSH D12.776.543.750 – receptors.2C cell surface

External links