Protein A magnetic beads can be used to capture antibodies from cell cultures. Adding the magnetic beads directly into the cell cultures and leaving them shaking overnight saves time and simplifies the capture procedure. But do the shaking magnetic beads harm the cells? We tested this by testing the viability of CHO cell culture after an overnight incubation with AmMag® protein A magnetic beads. We found that the viability of the cells is not significantly reduced.
|Culture flask||Medium volume (CHO cells)||speed||Before adding magnetic beads||Magnetic Beads volume||Magnetic beads/Culture (v/v)||After adding magnetic beads|
|250 mL||50 mL||100 rpm||6.12||100%||2.5 mL||5%||3.78||87.5%|
|50 mL||100 rpm||6.12||100%||1.25 mL||2.50%||7.16||96.76%|
|50 mL||100 rpm||6.12||100%||0.25 mL||0.50%||6.08||91.82%|
|50 mL||100 rpm||6.12||100%||0 mL||0%||6.36||96.36%|
|500 mL||50 mL||113 rpm||2.92||97.70%||2.5 mL||5%||3.7||98%|
|50 mL||113 rpm||2.97||97.40%||1.25 mL||2.50%||4.5||97.80%|
|50 mL||113 rpm||2.69||97.50%||0.25 mL||0.50%||3.66||96.30%|
|50 mL||113 rpm||2.64||96.40%||0 mL||0%||3.44||97.70%|
Should you reuse magnetic beads?
After one purification cycle, magnetic beads often retain sufficient ligands on their surface, which allows them to be reused for several additional rounds of purification. However, with each purification cycle, the beads become contaminated with cellular proteins, fats, and leftover target proteins that were not sufficiently eluted out. Therefore, magnetic beads can only be reused when cross-sample contamination is not a concern (for example, when the same target protein is purified again). Due to accumulation of impurities and leaching of ligands with each cycle of purification, a reduced binding capacity is observed with each round of reuse. The number of reuses may be determined experimentally, and is expected to be different for diverse types of sample preparations and magnetic beads. As an exception, GenScript’s AmMag® series of magnetic beads have extended ligand stability, and the immobilized ligands on these beads can withstand washes with 0.1 N sodium hydroxide. A wash with sodium hydroxide saponifies fats and dissolves proteins from the surface of the magnetic beads, and leaves the beads clean for multiple reuses with other samples. For example, the AmMag® protein A magnetic beads can be reused over 40 times, and the AmMag® Ni magnetic beads can be reused over 100 times without loss in binding capacity.