Modification of the immobilized metal affinity electrophoresis using sodium dodecyl sulfate polyacrylamide gel 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.

One-dimensional and two-dimensional immobilized metal affinity electrophoresis

Immobilized metal affinity electrophoresis (IMAEP) is a straightforward method in which metal ions are embedded in a polyacrylamide gel strip with a negligible electrophoretic migration. Due to the preferential binding between metal ions and the phosphate group, this method uses immobilized metal ions like iron, manganese, aluminum, or titanium to capture phosphoproteins from a mixture of phosphoprotein and nonphosphoproteins. IMAEP has also been incorporated into a traditional two-dimensional (2D) sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) system (isoelectric focusing-PAGE) to increase its resolving power. In 2D IMAEP, the metal ions in polyacrylamide gel strip are overlaid on top of the second dimensional polyacrylamide gel to stop electrophoretic migration of phosphoproteins. Data shows that there is no detrimental effect of SDS in IMAEP on the extraction of phosphoproteins from a mixture of proteins. In addition, SDS exposes phosphate groups by unfolding the phosphoproteins to facilitate metal ion-phosphate binding while supplying the protein with negative charges.

Separation and detection of large phosphoproteins using Phos-tag SDS-PAGE

We provide a standard phosphate-affinity SDS-PAGE (Mn(2+)-Phos-tag SDS-PAGE) protocol, in which Phos-tag is used to analyze large phosphoproteins with molecular masses of more than 200 kDa. A previous protocol required a long electrophoresis time of 12 h for separation of phosphoisotypes of large proteins ( approximately 150 kDa). This protocol, which uses a 3% (wt/vol) polyacrylamide gel strengthened with 0.5% (wt/vol) agarose, permits the separation of protein phosphoisotypes larger than 200 kDa within 2 h. In subsequent immunoblotting, phosphoisotypes of high-molecular-mass proteins, such as mammalian target of rapamycin (289 kDa), ataxia telangiectasia-mutated kinase (350 kDa) and p53-binding protein 1 (213 kDa), can be clearly detected as up-shifted migration bands on the improved Mn(2+)-Phos-tag SDS-PAGE gel. The procedure from the beginning of gel preparation to the end of electrophoresis requires about 4 h in this protocol.