What are Tyrosine kinases?
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell.
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 are cell-surface glycoproteins that bind specifically to cytokines and transduce their signals.
Cytokine receptors fall within five families (Based on 3 dimensional structures)
- Immunoglobulin superfamily receptors
- Class I cytokine receptor family (also known as the hematopoietin receptor family)
- Class II cytokine receptor family (also known as the interferon receptor family)
- TNF receptor family
- Chemokine receptor family (GPCR)
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
Different cytokine receptors evoke different cellular responses by activating different STATs.