Amino signal transduction

Noncatalytic phosphotyrosine binding (PTB) domains are 100-150 residue modules, which bind Asn-Pro-X-Tyr motifs. PTB-domain binding specificity is determined by residues at the amino-terminal side of the phosphotyrosine. In most cases, the tyrosine residue must be phosphorylated in order to mediate binding. PTB domain containing proteins are often found in signal transduction pathways. 

Weigele M, Bohacek R, Jacobsen VA, Macek K, Yang MG, Kawahata NH, Sundaramoorthi R, Wang Y, Takeuchi CS, Luke GP, Metcalf CA III, Shakespeare WC, Sawyer T. Synthesis of phosphono-containing amino acid derivatives and peptides as signal transduction inhibitors. PCT Int Appl W099/24442, 1999. 

The IFN-y receptor (the type II receptor) displays a more limited cellular distribution than that of the type I receptors (Table 8.5). This receptor is a transmembrane glycoprotein of molecular mass 50 kDa, which appears to function as a homodimer. The extracellular IFN-y binding region consists of approximately 200 amino acid residues folded into two homologous domains. Initiation of signal transduction also requires the presence of a second transmembrane glycoprotein known as AF-1 (accessory factor 1), which associates with the extracellular region of the receptor. 

The transmembrane domain in the RPTK is a hydrophobic segment of 22-26 amino acids inserted in the cell membrane. It is flanked by a proline-rich region in the N-terminus and a cluster of basic amino acids in the C-ter-minus. This combination of structures secures the transmembrane domain within the lipid bilayer. There is a low degree of homology in the transmembrane domain, even between two closely related RPTKs, suggesting that the primary sequence contains little information for signal transduction. 

Raloxifene is also anchored to the same three amino acids as estradiol by direct hydrogen bonds, but it also interacts with Asp 351. The final orientation of raloxifene within the binding pocket determines that its side chain displaces helix 12. Then, helix 12 becomes reoriented and cannot seal the pocket containing the ligand (MacGregor et al. 1998). The repositioned AF-2 region impairs the formation of transcription complex by coactivators, and the signal transduction is blocked. 

SH2 domains generally consist of approximately 100 amino acid residues [49,50, 60,61 ] and have been first identified as a conserved sequence region between the oncoproteins Src and Fps [19, 48]. By means of sequence homology, SH2 domains have been uncovered in numerous other intracellular signal transduction proteins (Figs. 1 and 4) [20]. 

A second well characterized signal transduction pathway, which is subject to lithium inhibition, is the phosphoinositol cascade (see Chapter 11, in particular Figure 11.8). A number of enzymes of this pathway contain a common amino acid sequence that constitutes a lithium-sensitive Mg2+ binding site, and it has been proposed that lithium exerts some of... 

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