Measuring Protein Tyrosine Phosphatase Activity Dependent on SH2 Domain-Mediated Regulation.

Src-homology-2 (SH2) domains bind selectively to phosphotyrosine (pTyr) residues located in target binding proteins; therefore, they are key elements in pTyr-mediated signaling pathways. The binding of an SH2 domain to a pTyr acts as a docking mechanism that attracts proteins into signaling hubs, and in some cases, it can also regulate the catalytic activity of signaling enzymes such as protein kinases or protein phosphatases. Therefore, compounds that selectively bind SH2 domains can be potentially used to modulate the activity of such SH2 domain-containing enzymes. This chapter describes how to measure the regulation of protein tyrosine phosphatase activity through allosteric binding of peptides to SH2 domains, and uses human recombinant protein tyrosine phosphatase SHP2 (Src homology-2 domain-containing protein tyrosine phosphatase 2) purified from bacteria as a case example. The phosphatase activity against the artificial substrate DiFMUP (6, 8-Difluoro-4-Methylumbelliferyl Phosphate) is measured over time in the presence of a peptide that selectively binds and activates SHP2 at different concentrations to determine the half maximal effective concentration (EC50).

Peptides as Baits for the Coprecipitation of SH2 Domain-Containing Proteins.

Phosphotyrosine (pTyr)-containing amino acid sequences have regulatory effects on proteins that contain pTyr recognition motifs, such as Src Homology 2 (SH2) domains. Using pTyr-containing peptides as a bait for coprecipitation, by immobilization of the synthesized phosphopeptides to beads and incubation with cell lysates, enables to study the binding preference of the SH2 domain for the specific pTyr-sequence obtained from a pTyr-containing protein in a complex biological environment. Using phosphopeptides allows to not only assess the wild-type sequence, but also peptides that can contain modified sequences which carry a nonhydrolyzable pTyr or other modifications varying the binding strength and selectivity, for example, to create strong SH2 domain binders to inhibit their interaction with pTyr-containing proteins. This pulldown experiment can be used as an assay to evaluate the ability of a peptide to bind to the protein of interest in the cell lysate or investigate the selectivity of the peptide. Therefore, immobilizing phosphopeptides and using them as a pulldown tool has a wide range of applications.

Novel Group of Imidazole Derivatives as Atypical Selective Cyclooxygenase-2 Inhibitors: Design, Synthesis and Biological Evaluation.

In this study, a new series of 5-substituted 1-benzyl-2-(methylsulfonyl)-1-H-imidazole with atypical structure-activity relationship was designed, synthesized, and biological evaluated as selective cyclooxygenase-2 inhibitors. Docking studies revealed that although the pharmacophoric substitute of the compound 5b, methylsulfonyl group, has been directly attached to the central ring, it is in the same direction of the sulfonamide group of Celecoxib, a known selective cyclooxygenase-2 inhibitor. Therefore effective hydrogen binding with Arg513 is established. Also, additional hydrogen binding could form between NH of anilino moiety of the 5b and Arg120. All of the compounds had selective inhibitory activity against cyclooxygenase-2 in micromolar concentrations comparable with the reference, Celecoxibe. Finally, compound 5b with the selectivity index 115 and IC50 of 0.71 µM against cyclooxygenase-2 was the most potent one.

A rapid HPLC method for determination of zolpidem and its degradation product in tablets using a monolithic column.

A simple, accurate reverse phase high-performance liquid chromatographic method, utilizing a monolithic silica column, for determination of zolpidem hemitartrate and its degradation product in tablet dosage form was developed. Analysis was achieved on the monolithic, C18 (100 mm, 3.9 mm) column, in isocratic mode with acetonitrile-NaH2PO4 (pH 7.0; 0.01 M; 35:65, v/v) as mobile phase and a flow rate of 2.5 mL/min at room temperature with UV detection at 245 nm. Diazepam was applied as an internal standard. The retention time of zolpidem and its degradation product was 2.14 and 1.89, respectively. Calibration curve was linear in the range of 0.12-5 µg/mL and the recovery values were found to be 97-101%. The limit of quantitation was determined 0.12 µg/mL. The relative standard deviation values of intraday and interday studies were calculated as 0.13-1.1% and 0.54-1.3%, respectively.