Magnetic beads for protein purification

Magnetic beads are used to purify single proteins, large protein complexes, antibodies and for high-throughput purifications. Magnetic beads based on chromatography resins provide functions of the resin with the convenience and ease-of-use of magnetic beads. Mag Sepharose beads, for example, are a convenient alternative to Sepharose columns. With a range of available ligands, these beads can simplify sample preparation of proteins and peptides prior to analysis.

Working with mag beads for protein purification

To begin with, it is important to adjust the volume of bead to protein in the starting material.

  • Insufficient affinity material will reduce binding capacity, and excess binding sites can amplify non-specific signals when sites are saturated.
  • If your biomolecule of interest is small, more will bind per bead than for larger biomolecules. 
  • When the antibody, tag or antigen is large, the volume of beads used can be increased to provide sufficient binding surface. 
  • Small bead size provides a greater surface area for binding and can also be used for large molecules to maximize binding capacity per bead.

For diluted samples like cell supernatants or low-abundance proteins, larger volumes of sample need to be applied to relatively smaller bead volumes, or the samples need to be concentrated. Alternatively, bead-sample incubation times can be increased. Glycerol applied to the samples might reduce non-specific binding. Select high-affinity tags (commonly used ones include GST, His and streptavidin) while ensuring they specifically express only in your protein of interest. Elute in a buffer having ligands with higher affinity for the beads than the specific protein, or with a buffer that has a higher pH.

Mag Sepharose—Attractive Sample Preparation

See a demo of a sample Mag Sepharose protocol: Mag Sepharose magnetic beads: Overview and demo