Since Stat3 initiates its signaling activity through binding of its SH2 domain to phosphotyrosine see more residues on cell surface receptors, inhibitors targeting this region of the protein are potential chemotherapeutic agents. To date, no NMR or X-ray crystallographic structures of high-affinity phosphopeptides complexed with the Stat3 SH2 domain are available to aid in the development of peptidomimetic antagonists. Examination of the crystal structures of several STAT proteins and the complex of Stat1 with Ac-pTyr-Asp-Lys-Pro-His-NH2 led to

a hypothesis that the specificity determinant for Stat3, glutamine at position pY+3 in pTyr-Xxx-Xxx-Gln sequences, resides in a unique pocket on the protein surface at the juncture of the third strand of the central beta-sheet and a unique, STAT specific alpha-helix. Docking of Ac-pTyr-Leu-Pro-Gln-NHBn to the SH2 domain of Stat3 using molecular modeling showed that the Gln binds tightly in this pocket and Ricolinostat order participates in a network of hydrogen bonds. Novel interactions between the peptide main chain and the protein were

also discovered. Phosphopeptide structure-affinity studies using unnatural amino acids and glutamine derivatives provide evidence for the peptide-protein interactions revealed by the model and lend support to the binding hypothesis. (C) 2007 Wiley Periodicals, Inc.”
“The key visual VX-770 purchase G protein, transducin undergoes bi-directional translocations between the outer segment (OS) and inner compartments of rod photoreceptors in a light-dependent manner thereby contributing to adaptation and neuroprotection of rods. A mammalian uncoordinated 119 protein (UNC119), also known as Retina Gene 4 protein (RG4), has been recently implicated in transducin transport to the OS in the dark through its interaction with the N-acylated GTP-bound transducin-alpha subunit (G alpha(t1)).

Here, we demonstrate that the interaction of human UNC119 (HRG4) with transducin is dependent on the N-acylation, but does not require the GTP-bound form of G alpha(t1). The lipid specificity of UNC119 is unique: UNC119 bound the myristoylated N terminus of G alpha(t1) with much higher affinity than a prenylated substrate, whereas the homologous prenyl-binding protein PrBP/delta did not interact with the myristoylated peptide. UNC119 was capable of interacting with G alpha(t1) GDP as well as with heterotrimeric transducin (G(t)). This interaction of UNC119 with G(t) led to displacement of G beta(1)gamma(1) from the heterotrimer. Furthermore, UNC119 facilitated solubilization of G(t) from dark-adapted rod OS membranes. Consistent with these observations, UNC119 inhibited rhodopsin-dependent activation of G(t), but had no effect on the GTP-hydrolysis by G alpha(t1).