Receptor (biochemistry)

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In biochemistry, a protein or a protein complex is referred to as a receptor (from the Latin recipere , `` to receive '' or `` to receive '') if signal molecules can bind to it, which are able to trigger signal processes inside the cell. A receptor can receive signals from outside and lie on the surface of a biomembrane or be in the cytosol of the cell. Receptors have a specific binding site for their physiological agonist .

Membrane receptors

Membrane receptors are located on the surface of biomembranes and consist of proteins that are often provided with additional modifications (e.g. carbohydrate chains ). They have a specific fit for small molecules, so-called ligands , or for parts of larger molecules that bind to the receptor structure by adding to it as a complementary structure (simply called the lock-and-key principle ).

Receptors can thus serve to take up signals ( signal transduction ), or to hold cells together ( cell adhesion ), or to transport substances into the cell ( membrane transport ). They can also offer virions the possibility of docking with the appropriate host cell and infecting them .

The membrane receptors that are important for cell contacts include cell adhesion molecules that mediate cell-cell contacts such as cadherins , selectins and immunoglobulins , as well as those that establish cell-matrix contacts and anchor cells to the extracellular matrix such as integrins .

Membrane receptors are not only found in the plasma membrane , but also in biomembranes of organelles inside cells . While external cell membrane receptors relate the cell to the external space as its environment, in the interior of the cell individual organelles are related to the cytoplasm , cytoskeleton or to each other via receptors .

Receptors in the cell membrane are divided into ionotropic and metabotropic receptors according to their mode of action .

  • Ionotropic receptors are ion channels that are more likely to open when the ligand binds, thereby changing the conductivity of the membrane.
  • Metabotropic receptors do not form channels or pores , but rather activate a downstream G protein or protein kinase when their ligand binds and thus modulate intracellular signal cascades by changing the concentration of secondary messenger substances. In addition, the membrane permeability can be changed indirectly.

Intracellular nuclear receptors

In addition, there are ligand- binding receptors of a cell, such as steroid receptors , which are not membrane-bound but are present in the cytoplasm or in the caryoplasm . These nuclear receptors can bind hydrophobic hormones such as the cholesterol derivative cortisol , or hydrophilic hormones such as the thyroid hormone thyroxine , and can be associated with other proteins (such as heat shock proteins ). A ligand binding causes a conformational change of the protein, which can expose its DNA-binding domain or activate the receptor already bound to DNA. This turns the receptor protein into a transcription factor that can change the expression of certain genes in the cell nucleus , be it as an activator or as a repressor of transcription .

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6th edition. Spectrum Academic Publishing House, Munich a. a. 2007, ISBN 978-3-8274-1800-5 .
  • Donald Voet, Judith G. Voet: Biochemistry. 4th edition. John Wiley & Sons, Hoboken NJ 2011, ISBN 978-0-470-57095-1 .
  • Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell. 4th edition. Garland, New York NY 2002, ISBN 0-8153-3218-1 .

Web links

Individual evidence

  1. ↑ P. Germain et al .: Overview of nomenclature of nuclear receptors . In: Pharmacol. Rev. . Volume 58, No. 4, December 2006, pp. 685-704. PMID 17132848 . PDF