Phosphorylation, serine/threonine

Rossomando, A. J., Saanghcra, J. S., Marsden, L. A., Weber, M. J., Pelech, S. L., and Sturgill, T. W. (1991). Biochemical characterization of a family of serine/threonine protein kinases regulated by tyrosine and serine/threonine phosphorylation. J. Biol. Chem. 266 20270-20275. 

Ohtake K, Maeno T, Ueda H, Ogihara M, Natsume H, Morimoto Y (2003) Poly-L-arginine enhances paracellular permeability via serine/threonine phosphorylation of ZO-1 and tyrosine dephosphorylation of occludin in rabbit nasal epithelium. Pharm Res 20 1838-1845. 

Ohara, O., Mann, M., Jensen, O. N., Pandey, a. (2002). A mass spectrometry-based proteomic approach for identification of serine/threonine-phosphorylated proteins by enrichment with phospho-spedfic antibodies identification of a novel protein, Frigg, as a protein kinase A substrate. Mol. Cell Proteomics 1, 517-527. 

Representative of upstream kinases which accept receptor signals are the Raf kinases. They are cytosolic Ser/Thr kinases. Raf kinase is recruited to the membrane and its activity is controlled by Ras. Raf phosphorylates and activates dual specificity, e.g. Ser/Thr-and Tyr-MAPKKs. The MAPKKs have a conserved serine/threonine phosphorylation site which is recognized and phosphorylated by Raf. 

In addition to the serine-threonine phosphorylation sites modulated by PKC and PKA, a basal state of tyrosine phosphorylation exists in platelet TP receptors, as in bradykinin receptors, and this phosphorylation increases on agonist stimulation (166). The tyrosine kinase responsible for this pho horylation, as well as that of the parallel phosphorylation of phosphatidylinositol 34dnase (PIj4dnase), that occurs on agonist stimulation, is unknown, but p27 known to be activated by TP receptor agonists (167), is a candidate (166). It is also possible that PI, kinase itself might phosphorylate TP receptors. The functional role of tyrosine kinase-mediated phosphorylation of TP receptors is unknown. 

Paz, K., Hemi, R., LeRoith, D., Karasik, A., Elhanany, E., Kanety, H., and Zick, Y. A molecular basis for insulin resistance. Elevated serine/threonine phosphorylation of IRS-1 and IRS-2 inhibits their binding to the juxtamembrane region of the insulin receptor and impairs their ability to undergo insulin-induced tyrosine phosphorylation. J. Biol. Chem.,... 

Phosphorylation of proteins on Ser/Thr residues is one of the most common regulatory modifications of signaling proteins (see Chapters 2 and 7). Only recently has it been recognized that serine/threonine phosphorylation results in the formation of multiprotein signaling complexes through specific interactions between phosphory-lated sequence motifs and the following phosphoserine/threonine-binding domains (review Yaffe and Elia, 2001). 

Singer KL, Stevenson BR, Woo PL, Firestone GL. Relationship of serine/threonine phosphorylation/dephosphorylation signaling to glucocorticoid regulation of tight junction permeability and ZO-1 distribution in nontransformed mammary epithelial cells. J Biol Chem 1994 269 16,108-16,115. 

Tzivion, G., and J. Avruch. 2002. 14-3-3 proteins active cofactors in cellular regulation by serine/threonine phosphorylation. J. Biol. Chem. 277 3061-3064. 

Inhibitors of serine/threonine phosphatases, such as okadaic acid or microcystin, can be used to investigate the effects of serine/threonine phosphorylation on kinase targeting. Tyrosine phosphatase inhibitors can be used to investigate the effect of tyrosine phosphorylation on kinase targeting in a specific cell type. For example, orthovanadate has been shown to induce translocation of the immunoreactivity of phospholipase C gamma from the cytosolic to the membrane fraction of mast cells (Atkinson et al, 1993). Conversely, in permeabilized preparations, the phosphatases themselves, if known, can be added to inhibit the putative pathway. 

Phosphorylation of the tyrosine residues on growth factor receptors and activation of Ras are both short-lived events. Phos-phoprotein phosphatases reverse the phosphorylation, and the GTP bound to Ras is rapidly hydrolyzed to GDP when a GAP (see Solved Problem 6.11) binds to Ras. Therefore, transducing these short-lived signals into longer-lived serine/threonine phosphorylations on MEK and MAP kinases allows the signal, which is initiated by binding of a growth factor to its receptor, to persist. The selection of a particular pathway is achieved at the level of the MAP kinases these are inactive unless they are phosphorylated on specific serine and tyrosine residues, and the only known substrates for MAP kinase kinases are MAP kinases. 

Tanti, J.-R, et al., Serine/threonine phosphorylation of insulin receptor substrate 1 modulates insulin receptor signaling, J. Biol Chem., 269, 6051, 1994. 

Countaway, J.L. et al.. Multisite phosphorylation of the epidermal growth factor receptor use of site-directed mutagenesis to examine the role of serine/threonine phosphorylation, J. Biol Chem., 265,3407,1990. 

Post-source Decay Tandem Mass Spectrometry The potential of PSD has also been exploited to identify phosphopeptides [61,62]. This technique is used for MALDI-generated ions in a reflectron TOP instrument. PSD can also distinguish any serine-threonine phosphorylation from tyrosine phosphorylation. Phosphotyrosine-containing peptides mostly yield the [MH — HP03J+ (loss of 80 Da) ion, whereas phosphoserine- and threonine-containing peptides produce [MH - H3P041+ (loss of 98 Da) and [M - HP03]+ ions. 

Ram PA, Park SH, Choi HK, Waxman DJ (1996) Growth hormone activation of Statl, Stat3, and Stat5 in rat liver. Differential kinetics of hormone desensitization and growth hormone stimulation of both tyrosine phosphorylation and serine/threonine phosphorylation. J Biol Chem 271 5929-5940... 

Protein kinase inhibitors (PKIs) provide a promising therapeutic strategy for cancer chemotherapy. Phosphorylation of proteins is a universal mechanism for the control of many cellular processes. The phosphorylation of proteins occurs when the y-phosphate group of ATP is transferred to either tyrosine or serine/threonine within proteins. One family of enzymes catalyses tyrosine phosphorylation and another serine/threonine phosphorylation. Tyrosine phosphorylation is up-regulated in tumour cells and thus provides a selective target for therapy. Although there are numerous protein kinase stmctures, they have some features in common and the active site of the enzyme consists... 

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