Dimerization of tyrosine

In animal structural proteins in vivo, the only known dimer of tyrosine is dityrosine (40,41) in the extensin of plant cell walls, in contrast, the only dimer formed in vivo is isodityrosine (16). How is the coupling of tyrosine in plants confined to the formation of isodityrosine There is nothing unique about the local environment of the tyrosine residues in (pure) extensin, since... 

These oxidation was perfectly suppressed by the addition of EDTA(0. ImM), catalase(500units/mL) and aminoguanidine(10mM) and so it suggests that the dimerization of tyrosine evidently proceeds with radical reaction. Dityrosine has been... 

II cleaves the two complementary strands of DNA four base pairs apart and the resulting 5 -phosphoryl groups become covalently linked to a pair of tyrosine groups, one in each half of the dimeric topoisomerase II enzyme. Several groups of drugs are known that selectively inhibit topoisomerases in bacteria (quino-lones) or mammalian cells (etoposide, tenoposide). Quinolones are used to treat bacterial infections inhibitors of mammalian topoisomerases are cytostatic drugs used for the treatment of cancer. 

In principle, RTK autophosphorylation could occur in cis (within a receptor monomer) or in trans (between two receptors in a dimer). In the first case, ligand binding would cause a change in receptor conformation that would facilitate c/ s-autophosphorylation of tyrosine residues located within or outside the PTK domain. In the second case, no conformational change must occur upon dimerization. The simple proximity effect would provide sufficient opportunity for trans-phosphorylation of tyrosines in the cytoplasmic domain by a second RTK. 

Tertoolen, L. G., Blanchetot, C., Jiang, G., Overvoorde, J., Gadella, T. W., Jr., Hunter, T. and den Hertog, J. (2001). Dimerization of receptor protein-tyrosine phosphatase alpha in living cells. BMC Cell Biol. 2, 8. 

It is worth mentioning that membrane-bound forms of GC, which can be considered signal transducing enzymes , are structurally homologous to other signal transducing enzymes, such as certain protein tyrosine kinases and phosphatases, which also possess receptor moieties in their extracellular (amino terminus) domain and enzyme catalytic activity in their intracellular domain (see Ch. 24). Activation of many of these receptors occurs upon ligand-induced dimerization of the receptors, and a similar... 

Insulins (see p. 388), growth factors, and cytokines (see p. 392), for example, act via 1-helix receptors. Binding of the signaling substance leads to activation of internal kinase activity (in some cases, dimerization of the receptor is needed for this). The activated kinase phosphorylates itself using ATP (auto-phosphorylation), and also phosphorylates tyrosine residues of other proteins (known as receptor substrates). Adaptor proteins that recognize the phosphotyrosine residues bind to the phosphorylated proteins (see pp. 388, 392). They pass the signal on to other protein kinases. 

In contrast to the receptors for insulin and growth factors (see p. 388), the cytokine receptors (with a few exceptions) have no tyrosine kinase activity. After binding of cytokine (1), they associate with one another to form homodimers, join together with other signal transduction proteins (STPs) to form dimers, or promote dimerization of other... 

Lenferink, A. E., R. Pinkas Kramarski, M. L. van de Poll, M. J. van Vugt, L. N. Klapper, E. Tzahar, H. Waterman, M. Sela, E. J. van Zoelen, and Y. Yarden. Differential endocytic routing of homo- and hetero-dimeric ErbB tyrosine kinases confers signaling superiority to receptor heterodimers. EMBO J. 17 3385-3397.1998. 

The basic extensins. These are hydroxyproline-, lysine- and tyrosine-rich glycoproteins consisting of rigid molecular rods about 80 nm long (14,15), bearing short mono- to tetrasaccharide side-chains (2,14). When newly secreted they bind ionically to the acidic polysaccharides of the cell wall and can be extracted with cold salt solutions later they become much more resistant to salt-extraction and are said to be covalently bound, probably via dimerization of their tyrosine residues to form isodityrosine (15). 

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