Phosphorylation G proteins

Activator proteins themselves can be boimd in regulatory networks, as shown in the example of the cyclins (chapter 14). The function of an activator protein can be regulated at the level of gene expression, degradation, or post-translational modification (e.g. protein phosphorylation). 

The signal transmission by the hormone-receptor complex can be actively inhibited via covalent modifications (e.g. protein phosphorylation) which deactivate the hormone-receptor complex. Another mechanism for termination of signaling pathways is the... 

Tyrosine Kinase A large group of enzymes involved in intracellular signal transduction, which catalyzes the phosphorylation of tyrosine residues in target proteins. See Hardle, D.G., Protein Phosphorylation A Practical Approach, Oxford University Press, Oxford, UK, 1993 Woodgett, J.R., Protein Kinases, IRL Press, Oxford, UK, 1994 Hardle, D.G. and Hanks, S., Eds., The Protein Kinase Facts Book, Academic Press, San Diego, CA, 1995 Krauss, G., Ed., Protein Kinase Protocols, Wiley-VCH, Weinheim, Germany, 2003. 

The signal transmission by the hormone-receptor complex can be actively inhibited via covalent modifications (e.g., protein phosphorylation) which deactivate the hormone-receptor complex. Another mechanism for termination of signaling pathways is the internalization of the hormone-receptor complex. During internalization a section of the membrane, together with the proteins bound to it, is pinched off and transported into the interior of the cell. There the receptor can be returned to the cell membrane or be degraded. The internalization can affect the free receptor as well as the hormone-receptor complex. 

The nucleotide form of ribavirin does not manifest its antiviral activity simply by lowering the GTP levels, but may indeed participate directly in binding to specific G proteins (124). Ribavirin has recently been studied as an inhibitor of vesicular stomatitis vims and La Crosse vims (125). Of the phosphorylated forms of the dmg, ribavirin-5 -diphosphate was by far the most potent inhibitor of viral repHcation for these two vimses. 

E. G protein-conpled receptors /3-Adrenergic receptor kinase (BARK) Rhodopsin kinase II. Ser/Thr/Tyr protein kinases MAP kinase kinase (MAPK kinase) —TEY— phosphorylation by... 

The majority of functional assays involve primary signaling. In the case of GPCRs, this involves activation of G-proteins. However, receptors have other behaviors— some of which can be monitored to detect ligand activity. For example, upon stimulation many receptors are desensitized through phosphorylation and subsequently taken into the cell and either recycled back to the cell surface or digested. This process can be monitored by observing ligand-mediated receptor internalization. For... 

The ETa receptor activates G proteins of the Gq/n and G12/i3 family. The ETB receptor stimulates G proteins of the G and Gq/11 family. In endothelial cells, activation of the ETB receptor stimulates the release of NO and prostacyclin (PGI2) via pertussis toxin-sensitive G proteins. In smooth muscle cells, the activation of ETA receptors leads to an increase of intracellular calcium via pertussis toxin-insensitive G proteins of the Gq/11 family and to an activation of Rho proteins most likely via G proteins of the Gi2/i3 family. Increase of intracellular calcium results in a calmodulin-dependent activation of the myosin light chain kinase (MLCK, Fig. 2). MLCK phosphorylates the 20 kDa myosin light chain (MLC-20), which then stimulates actin-myosin interaction of vascular smooth muscle cells resulting in vasoconstriction. Since activated Rho... 

G-protein-coupled receptor kinases (GRKs) are a family of enzymes that catalyze the phosphorylation of threonine or serine residues on G-protein-coupled receptors. Characteristically, GRKs only phosphorylate the ligand-activated form of the receptors. Phosphorylation by GRKs usually leads to impaired receptor/G-protein coupling. 

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