(25) 921-946 enzyme coupled receptors

(25) 921-946 enzyme coupled receptors - S IGNAL ING THROUGH...

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SIGNALING THROUGH ENZYME COUPLED CELL SURFACE RECEPTORS Activated receptor tyrosine kinases phosphorylate themselves o GPCRs are transmembrane proteins o Enzyme-coupled receptors are also transmembrane proteins o Enzyme-coupled receptors have their ligand binding domain on the outer surface of the membrane o GPCR has 7 transmembrane segments o Enzyme-coupled receptor has only one o There are 6 classes of enzyme-coupled receptors: Receptor tyrosine kinases Directly phosphorylate tyrosines on themselves Tyrosine-kinase associated receptors Directly recruit cytoplasmic tyrosine kinases to relay the signal Receptor serine/threonine kinases Directly phosphorylate specific serines or threonines on themselves o Many extracellular signal proteins act through RTKs o For a GPCR, ligand binding changes the orientation of several of the transmembrane alpha helices, shifting position of loops o But for RTKs, ligand binding causes the receptor chains to dimerize, bringing the kinase domains of 2 receptor chains together so that they can become activated and cross-phosphorylate each other on multiple tyrosines (transautophosphorylation) o Ligand binding causes the two green receptors to dimerize, then the 2 kinase domains cross-phosphorylate each other, increasing the activity of the kinase domains, which now phosphorylate other sites on the receptors
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o Dominant-negative regulation – one of the tyrosine kinase domains is mutant and doesn’t work Phosphorylated tyrosines on RTKs serve as docking sites for intracellular signaling protein o Phosphorylation of tyrosines within the kinase domain increases the kinase activity of the enzyme o Phosphorylation of tyrosines outside the kinase domain creates high- affinity docking sites for the binding of specific intracellular signaling proteins, which bind to the RTK o Binding to RTK activates the docked signaling protein o Use IRS1 to create more docking sites Proteins with SH2 domains bind to phosphorylated tyrosines o These proteins help to relay the signal onwards. o
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This note was uploaded on 12/30/2010 for the course BIO 320 taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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(25) 921-946 enzyme coupled receptors - S IGNAL ING THROUGH...

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