Tyrosine kinases and cytokine receptors

What are Tyrosine kinases?

A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell.

Two types:

Receptor tyrosine kinases: The receptor itself has tyrosine kinase activity

  • The receptor tyrosine kinases are not only cell surface transmembrane receptors, but are also enzymes having kinase activity resides in their cytosolic kinase domain.
  • The kinase domain of the receptor catalyzes the transfer of a phosphate group from a nucleoside triphosphate donor (ATP) to tyrosine residues in proteins.

Eg: EGFR, PDGFR etc

Non receptor tyrosine kinases: Cytosolic enzymes that are responsible for catalyzing the transfer of a phosphate group from a nucleoside triphosphate donor (ATP) to tyrosine residues in proteins.

Examples: ZAP70, JAK family, SRC family, ABL family etc

JAK are usually associated with cytokine receptors

Cytokine receptors

Cytokine receptors are cell-surface glycoproteins that bind specifically to cytokines and transduce their signals.

Cytokine receptors fall within five families (Based on 3 dimensional structures)

  1. Immunoglobulin superfamily receptors
  2. Class I cytokine receptor family (also known as the hematopoietin receptor family)
  3. Class II cytokine receptor family (also known as the interferon receptor family)
  4. TNF receptor family
  5. Chemokine receptor family (GPCR)
Figure1: Schematic diagrams showing the structural features that define the five types of receptor proteins to which most cytokines bind. The receptors for most of the interleukins belong to the class I cytokine receptor family (C refers to conserved cysteine).

Cytokine receptors have no intrinsic tyrosine kinase activity.

Class I and Class II cytokine receptors are associated with cytoplasmic tyrosine kinases called JAKs that are activated when a cytokine binds to its receptor.

The most-studied class I cytokine receptors are the growth hormone receptor (GHR) and erythropoietin receptor (EPOR).

Refer: Erythropoietin signaling cascade

Link: http://easylifescienceworld.com/jak-stat-signaling-pathway/

Different cytokine receptors evoke different cellular responses by activating different STATs.

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