RET Proto-oncogene - Kinase Activation

Kinase Activation

RET is the receptor for members of the glial cell line-derived neurotrophic factor (GDNF) family of extracellular signalling molecules or ligands (GFLs).

In order to activate RET GFLs first need to form a complex with a glycosylphosphatidylinositol (GPI)-anchored co-receptor. The co-receptors themselves are classified as members of the GDNF receptor-α (GFRα) protein family. Different members of the GFRα family (GFRα1-GFRα4) exhibit a specific binding activity for a specific GFLs. Upon GFL-GFRα complex formation, the complex then brings together two molecules of RET, triggering trans-autophosphorylation of specific tyrosine residues within the tyrosine kinase domain of each RET molecule. Tyr900 and Tyr905 within the activation loop (A-loop) of the kinase domain have been shown to be autophosphorylation sites by mass spectrometry. Phosphorylation of Tyr905 stabilizes the active conformation of the kinase, which, in turn, results in the autophosphorylation of other tyrosine residues mainly located in the C-terminal tail region of the molecule.

The structure shown to the left was taken from the protein data bank code 2IVT. The structure is that of a dimer formed between two protein molecules each spanning from amino acids 703-1012 of the RET molecule, covering RETs intracellular tyrosine kinase domain. One protein molecule, molecule A is shown in yellow and the other, molecule B in grey. The activation loop is coloured purple and selected tyrosine residues in green. Part of the activation loop from molecule B is absent.

Phosphorylation of Tyr981 and the additional tyrosines Tyr1015, Tyr1062 and Tyr1096 not covered by the above structure, have been shown to be important to the initiation of intracellular signal transduction processes.