Enzyme-Coupled Receptors

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In enzyme-coupled receptors is transmembrane proteins and a receptor type , to the binding of a ligand , a signal transduction initiates.

properties

Enzyme-coupled receptors are one of the three main types of receptors besides ion channel- coupled receptors and G-protein-coupled receptors . The enzyme- coupled receptors are further divided into different subtypes.

Receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are receptors bound to the cell membrane , which usually have a transmembrane α-helix . The binding of a ligand activates the intracellular location tyrosine - domain , which thereafter ATP - hydrolysis of phosphate groups on tyrosine - radicals transfers. Mostly there is a dimerization or oligomerization (or a reorientation of the receptor in the case of already oligomeric proteins), which allows the receptors to phosphorylate one another ( autophosphorylization ). This process is primarily held responsible for signal routing.
Examples of ligands (or signal transduction pathways or protein activation) that proceed via a receptor tyrosine kinase:

Tyrosine Kinase Coupled Receptors

The tyrosine kinase-coupled receptors exert their signaling activity indirectly. They recruit tyrosine kinases dissolved in the cytoplasm , which then phosphorylate numerous other proteins after ligand binding of the receptor. These receptors work in a similar way to receptor tyrosine kinases, except that the kinase domain is not on the receptor itself, but on a non- covalently bound external protein. Examples of ligands (or signal transduction pathways or protein activation) that run via a tyrosine kinase-coupled receptor:

Tyrosine phosphatases

Tyrosine phosphatases can also act as transmembrane receptors and play z. B. an important role in the activation of T and B lymphocytes by the CD45 protein or in the deactivation of the JAK / STAT response by SHP 1 and 2. They partially exercise their role in the activation of a signal path by that they are deactivated by the ligand and thus no longer have an inhibitory effect on the signal path. This can also happen together with the tyrosine kinases, which, when activated, attach more phosphate groups to a certain protein, while the tyrosine phosphatases split off fewer phosphate groups, which leads to an even stronger activation overall.

Receptor Serine / Threonine Kinases

The receptor serine / threonine kinases are mainly active in the TGF signaling pathway , which is stimulated by the growth factors of the TGF-β family . Two types of receptor serine / threonine kinases can be distinguished (type I and type II), whereby the ligand always binds the type II receptor first, which then forms a heterodimer with a type I receptor and forwards the signal (e.g. are Smad proteins activated).

Receptor guanylyl cyclases

The receptor guanylyl cyclases (see also: guanylyl cyclase ) have a guanylyl domain and, after activation, produce cyclic GMP , which acts as a second messenger . This in turn activates the cGMP-dependent protein kinase ( PKG ) which further phosphorylates proteins and thus forwards the signal. Ligands include natriuretic peptides ( ANP and BNP ), which play a role in regulating blood pressure .

Histidine Kinase Coupled Receptors

Histidine kinase-coupled receptors (see also: Histidine kinase ) are mainly found in plants and bacteria , but not in animals . They play an important role in chemotaxis and help the bacteria swim in a consistent direction.

Signaling pathways based on proteolysis

Signaling pathways based on proteolysis (cutting up of proteins) are diverse and play a role primarily in embryogenesis and in the development of cancer . Important representatives are:

Individual evidence

  1. ↑ Bruce Alberts: Molecular Biology of the Cell, Sixth Edition. Garland Science, 2014, ISBN 978-1-317-56375-4 , p. 818.