Tyrosine signalling

Miscellaneous Applications of EPR to PS II. - A number of authors used EPR to detect changes of the S-state cycle and the tyrosine radicals and correlated this with other functional aspects of the OEC and PS II. In particular, the prominent S2 state MLS and the tyrosine signals have been used for these investigations. A representative fraction of such work and some other EPR applications from the last years are discussed below. 

DAPIO, for instance) (Diefenbach andRaulet, 2003 Held etal., 2003). ITIMs with phosphorylated tyrosines signal inhibition through the recruitment and activation of the SHP-1 phosphatase ITAMswith phosphorylated tyrosines signal activation through the recruitment of Syk or ZAP70 tyrosine kinases. 

Collison K, Saleh S, Parhar R, Meyer B, Kwaasi A, Al-Hussein K, Al-Sedairy S, Al-Mohanna F Evidence for IL-12-activated Ca + and tyrosine signaling pathways in human neutrophils. J Immunol 1998 161 3737-3745. 

The last part of this account will be devoted to protein kinases and protein phosphatases and some recent results we have obtained for them. Protein kinases and phosphatases are signaling biomolecules that control the level of phosphorylation and dephosphorylation of tyrosine, serine or threonine residues in other proteins, and by this means regulate a variety of fundamental cellular processes including cell growth and proliferation, cell cycle and cytoskeletal integrity. 

There are five known classes of enzyme-linked receptors (1) receptor tyrosine kinases, which phosphorylate specific tyrosine residues on intracellular signaling proteins (2) tyrosine kinase-associated receptors, such as the prolactin and growth hormone receptors we have already discussed, which... 

Myristic acid may be linked via an amide bond to the a-amino group of the N-terminal glycine residue of selected proteins (Figure 9.18). The reaction is referred to as A -myristoylation and is catalyzed by myristoyl—CoAtprolein N-myris-toyltransferase, known simply as NMT. A -Myristoyl-anchored proteins include the catalytic subunit of cAMP-dependent protein kinase, the ppSff tyrosine kinase, the phosphatase known as calcineurin B, the a-subunit of G proteins (involved in GTP-dependent transmembrane signaling events), and the gag proteins of certain retroviruses, including the FHV-l virus that causes AIDS. 

The abundance of many protein kinases in cells is an indication of the great importance of protein phosphorylation in cellular regulation. Exactly 113 protein kinase genes have been recognized in yeast, and it is estimated that the human genome encodes more than 1000 different protein kinases. Tyrosine kinases (protein kinases that phosphorylate Tyr residues) occur only in multicellular organisms (yeast has no tyrosine kinases). Tyrosine kinases are components of signaling pathways involved in cell-cell communication (see Chapter 34). 

In general terms, cross talk refers to the interaction between signalling pathways, e.g. between pathways involving heterotrimeric GTP-binding proteins and tyrosine kinase pathways. 

Ephrins are a group of membranous ligands, which function through a family of receptor tyrosine kinases (Ephs). Ephrin/Eph-mediated signaling processes are involved in morphogenetic processes taking place e.g. during the development of the nervous system or the vasculature. 

Fyn is a nonreceptor tyrosine kinase related to Src that is frequently found in cell junctions. Die protein is N-myristoylated and palmitoylated and thereby becomes associated with caveolae-like membrane microdomains. Fyn can interact with a variety of other signaling molecules and control a diversity of biological processes such as T cell receptor signaling, regulation of brain function, and adhesion mediated signaling. 

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