Src homology-2 (SH2) domains recognize specific phosphotyrosyl (pY) proteins and promote protein-protein interactions. In their classical binding mode, the SH2 domain makes specific contacts with the pY residue and the three residues immediately C-terminal to the pY, although for a few SH2 domains, residues N-terminal to pY have recently been shown to also contribute to the overall binding affinity and specificity. In this work, the ability of an SH2 domain to bind to the N-terminal side of pY has been systematically examined. A pY peptide library containing completely randomized residues at positions -5 to -1 (relative to pY, which is position 0) was synthesized on TentaGel resin and screened against the four SH2 domains of phosphatases SHP-1 and SHP-2. Positive beads that carry high-affinity ligands of the SH2 domains were identified using an enzyme-linked assay, and the peptides were sequenced by partial Edman degradation and matrix-assisted laser desorption ionization mass spectrometry. The N-terminal SH2 domain of SHP-2 binds specifically to peptides of the consensus sequence (H/F)XVX(T/S/A)pY. Further binding studies with individually synthesized pY peptides show that pY and the five residues N-terminal to pY, but not any of the C-terminal residues, are important for binding. The other three SH2 domains also bound to the library beads, albeit more weakly, and the selected peptides did not show any clear consensus. These results demonstrate that at least some SH2 domains can bind to pY peptides in an alternative mode by recognizing only the residues N-terminal to pY.
Aromatic azo derivatives possess a particular character that is the light driven reversible isomerization between their cis-and trans-forms, which makes them excellent candidates to modulate the relative movement of different moieties. They are widely used not only in the traditional chemical industry, but also in many newly rising areas of science, such as photochemical molecular switch, super-molecular chemistry of host-guest recognition, self-assembly liquid crystal material, analysis of biomedical imaging and chemical, light driven molecular motor, and so on. The development of chromophores with characteristics, like high chemical stability, thermal stability over a wide temperature range and having two forms easily detectable by a method that does not cause irreversible molecular alterations, is a major challenge for researchers who focus their interest in this area. With the increasing need for investigating unknown aromatic azo derivatives, many novel efficient synthesis strategies are recently innovated and developed in succession. This critical review covers the various synthetic methods of aromatic azo derivatives reported more recently, with special emphasis on application of arylhydrazine, arylamine, nitroarene, azoxyarene, arylazide, and their derivatives.
The fabrication and adsorption mechanism of flower-like MoS2/g-C3N4 nanocomposites as new adsorbent materials were investigated by batch sorption experiments in this paper. The influence of factors such as pH, adsorbent dosage, concentration and temperature on the adsorption properties of flower-like MoS2/g-C3N4 nanocomposites were studied in detailed. The adsorption isotherm data was fitted with the Langmuir model, and the adsorption kinetic characteristics conform to the quasi second-order kinetic equation. Thermodynamic data showed that the adsorption process of methylene blue (MB) was feasible, endothermic and spontaneous. At 45 ℃, the maximum adsorption capacity was 278.4 mg/g. The adsorbed MB solution was used to water the wheat and chickpea plants within 15 days. Compared with MB solution, the treated MB solution made the plants grow much more better.
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