Catching and separating protein ligands by functional affinity electrophoresis

Applications of Immobilized Metal Affinity Electrophoresis

Immobilized metal affinity electrophoresis (IMAEP) is a technique in which metal ions are integrated in a localized polyacrylamide gel section and which possess an insignificant electrophoretic migration. IMAEP has been implemented into both native and sodium dodecyl sulfate (SDS) one-dimensional (1-D) and two-dimensional (2-D) polyacrylamide gel electrophoresis (PAGE) systems. The gel piece containing metal ions is overlaid on top of an individual well in 1-D IMAEP, and gel strip is overlaid on top of the two-second dimensional polyacrylamide gel in 2-D IMAEP, respectively. This method is used to capture/enrich metal ion binding proteins. Due to the preferential binding between iron (III), manganese (II), or aluminum (III) ions and the phosphate group, these metal ions are used to capture/enrich phosphoproteins from a mixture of proteins. Data shows that SDS not only does not interfere with the extraction of phosphoproteins but also help unmasking phosphate groups by unfolding the phosphoproteins to facilitate metal ion-phosphate binding while supplying the protein with negative charges. In addition, IMAEP together with avidin functional affinity electrophoresis (AFAEP) and antibody affinity electrophoresis (AAEP) have been used to demonstrate the separation of proteins by their functionalities. AFAEP is used here to capture biotinylated proteins using avidin and AAEP is used here to capture protein G using IgG.

Capturing biotinylated proteins and peptides by avidin functional affinity electrophoresis

Avidin functional affinity electrophoresis (AFAEP) is a variational method of affinity electrophoresis. In this technique, avidin is immobilized within a small area of the gel matrix by interaction with acrylamide and/or polyacrylamide either directly or through bifunctional linker glutaraldehyde during polymerization. Analytes can be heated with Tris-glycine sodium dodecyl sulfate (SDS) sample buffer so that biotinylated peptides/proteins are negatively charged and migrate electrophoretically towards the cathode through the avidin zone regardless of their isoelectric point (pI) values. Alternatively, if the behavior of the biotinylated analytes is known, the SDS treatment is not required. The polarity of the electrodes is set such that biotinylated analytes migrate electrophoretically through the avidin zone. This technique can work with or without SDS in gel running buffer. The AFAEP method allows the capture and concentration of biotinylated peptides/proteins. The values of this technique stem from a combination of merits of polyacrylamide gel electrophoresis and affinity technology.

Dynamic receptor-dependent activation of inducible nitric-oxide synthase by ERK-mediated phosphorylation of Ser745

Nitric oxide (NO) is a pleiotropic regulator of vascular function, and its overproduction by inducible nitric-oxide synthase (iNOS) in inflammatory conditions plays an important role in the pathogenesis of vascular diseases. iNOS activity is thought to be regulated primarily at the level of expression to generate "high output" NO compared with constitutive NO synthases. Here we show iNOS activity is acutely up-regulated by activation of the B1-kinin receptor (B1R) in human endothelial cells or transfected HEK293 cells to generate 2.5-5-fold higher NO than that stimulated by Arg alone. Increased iNOS activity was dependent on B1R activation of the MAPK ERK. In HEK293 cells transfected with human iNOS and B1R, ERK phosphorylated iNOS on Ser745 as determined by Western analysis using phospho-Ser antibody, in vitro kinase assays with activated ERK, and MALDI-TOF mass spectrometry. Mutation of Ser745 to Ala did not affect basal iNOS activity but eliminated iNOS phosphorylation and activation in response to B1R agonist. Mutation of Ser745 to Asp resulted in a basally hyperactive iNOS whose activity was not further increased by B1R agonist. ERK and phospho-ERK (after B1R activation) were co-localized with iNOS as determined by confocal fluorescence microscopy. Furthermore, ERK co-immunoprecipitated with iNOS. The discovery that iNOS can be phosphorylated by ERK and acutely activated by receptor-mediated signaling reveals a new level of regulation for this isoform. These findings provide a novel therapeutic target to explore in the treatment of vascular inflammatory diseases.