Polyacrylamide Gel Affinity Electrophoresis for Separation of Enzyme Isoforms

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.

Mass spectrometric detection of biotinylated peptides captured by avidin functional affinity electrophoresis

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to detect biotinylated peptides captured by avidin functional affinity electrophoresis (AFAEP). Peptide samples loaded onto AFAEP were heated with sodium dodecyl sulfate to ensure that the peptides are negatively charged, and thus migrate electrophoretically toward the cathode through the embedded avidin zone in the middle of the gel. To detect the biotinylated peptides, the band containing the avidin-biotinylated peptide complexes was excised from a 7.5% w/v native polyacrylamide gel, and biotinylated peptides were extracted with aqueous 95% v/v formamide (pH 8.2), aqueous 6 M guanidine HCl (pH 1.5), or water, at temperatures from 4 to 95 degrees C for periods from 5 min to 24 h. It was observed that all three solvents are capable of extracting biotinylated peptides and avidin from the gel, but the best results were obtained with aqueous 95% v/v formamide (pH 8.2) at 65 degrees C for 20 min. However, some AFAEP-captured biotinylated peptides are not stable and are extensively modified by formamide during extraction at too high a temperature or too long an extraction time.

Catching and separating protein ligands by functional affinity electrophoresis

A new kind of affinity electrophoresis called functional affinity electrophoresis (FAEP) is a technique used to separate and/or capture proteins according to their functions in a native polyacrylamide gel. Protein A:immunoglobulin G, avidin:biotin, antibody:antigen, and concanavalin A:glycoprotein interactions are used to demonstrate this technique. Protein A, avidin, monoclonal anti-bovine serum albumin (BSA) antibody, and concanavalin A are embedded in distinct regions of a 7.5% native polyacrylamide gel. Some of each of the embedded proteins get covalently and/or noncovalently incorporated into the gel matrix network. Under electrophoresis conditions, these proteins do not show significant electrophoretic mobility or they migrate in a direction opposite to the protein analytes, as in avidin. We clearly observe that polyclonal anti-human myoglobin antibody, biotinylated insulin, BSA, and ovalbumin (glycoprotein) are captured and separated in distinct regions of a FAEP gel by protein A, avidin, monoclonal anti-BSA antibody, and concanavalin A, respectively.

Catching protein antigens by antibody affinity electrophoresis

A new kind of affinity electrophoresis called antibody affinity electrophoresis is a technique used to capture protein antigens based on their interactions with specific monoclonal or polyclonal antibodies incorporated in the polyacrylamide gel. Polyclonal anti-glutathione-S-transferase (anti-GST), monoclonal anti-bovine serum albumin (anti-BSA), and polyclonal anti-human alpha-lactalbumin are embedded in distinct areas of a 7.5% native polyacrylamide gel. Some of the embedded antibodies get covalently and/or noncovalently incorporated into the gel matrix network. Under electrophoresis conditions, these antibodies do not show significant electrophoretic mobility, as compared to their specific protein antigen analytes. We observed that electrophoretic migration of GST, BSA, and protein G ceases when they encounter anti-GST, anti-BSA, and immunoglobulin G, respectively.