What does autophosphorylation mean? When a receptor tyrosine kinase binds Its li

Question

What does autophosphorylation mean? When a receptor tyrosine kinase binds Its ligand and forms a dimer, do the individual receptor molecules phosphorylate themselves or does one receptor crossphosphorytate the other, and vice versa? To investigate this question, you have constructed genes for three forms of a receptor tyrosine kinase: the normal form with an active kinase domain and three sites of phosphorylation; a large form that carries an inactivating point mutation in the kinase domain but retains the three phosphorylation sites, and a short version that has an active kinase domain but is lacking the sites of phosphorylation (see figure A). You express the genes singly and in combination in a cell line that lacks this receptor tyrosine kinase, and then break open the cells and add the ligand for the receptor and in the presence of radioactive ATP. You immunoprecipitate the receptors and analyze them for expression levels by staining for protein (figure B) and for phosphorylation by autoradiography (figure C). What results expect on the autoradiography if individual receptors phosphorylated themselves? What would you expect if receptors cross-phosphorylated each other? Which model for autophosphorylation does your data support?

Explanation / Answer

a)If indivisual receptors phosphorylated themselves then only the band which corresponds to the normal receptor which has a functional kinase domain and phosphorylation will be present on the audiograph.

b)If the receptors cross phosphorylated themselves then normal receptors are labelled along with the mutant receptor 2 which includes a dead kinase domain which has a function phosphorylation sites which is labelled and it represents the active kinase domain.

c)The receptor 1 will pair will itself roughly half the time leading to cross phosphorylation,The model supporting this is the protein gel model as it shows the same.

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