Activation of the G Protein Gq/11 Through Tyrosine Phosphorylation of the α Subunit

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Abstract
Various receptors coupled to the heterotrimeric guanine nucleotide-binding protein Gq/11 stimulate formation of inositol-1,4,5-trisphosphate (IP 3 ). Activation of these receptors also induces protein tyrosine phosphorylation. Formation of IP 3 in response to stimulated receptors that couple to Gq/11 was blocked by protein tyrosine kinase inhibitors. These inhibitors appeared to act before activation of Gq/11. Moreover, stimulation of receptors coupled to Gq/11 induced phosphorylation on a tyrosine residue (Tyr 356 ) of the Gα q/11 subunit, and this tyrosine phosphorylation event was essential for Gq/11 activation. Tyrosine phosphorylation of Gα q/11 induced changes in its interaction with receptors. Therefore, tyrosine phosphorylation of Gα q/11 appears to regulate the activation of Gq/11 protein.
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