IgG and Fc-Protein Purification Using Protein A Resin

Materials Needed

Reagents

• Protein A agarose resin (Cat.# 700201)
• Phosphate Buffered Saline (PBS)
• PBS containing 0.09% sodium azide (optional)
• 0.1 M glycine, pH 2.7 (elution buffer)
• 2 M Tris-HCl, pH 8.0 (neutralization buffer)
• Deionized water

Equipment

• Gravity flow column (e.g., chromatography column)
• Tube rotator or stir plate (for batch purification)
• Collection tubes
• UV spectrophotometer or Bradford assay reagents
• Centrifuge or filtration unit for sample clarification

Protocol

1. Sample Preparation
   1. Collect cell culture supernatant or lysate containing IgG or Fc-tagged protein.
   2. Clarify the sample by centrifugation (e.g., 10,000 × g for 10–15 minutes) or filtration (0.45 μm).
   3. Keep the clarified sample on ice until purification.
2. Resin Preparation
   1. Gently invert the Protein A resin container to fully resuspend the beads.
   2. Transfer the desired volume of resin to an empty column.
   3. Allow the resin to settle by gravity.
   4. Drain the storage buffer completely without allowing the resin to dry.
   5. Wash the resin with at least 2 column volumes (CV) of PBS (or PBS with 0.09% sodium azide) to remove residual ethanol.
   The resin is now equilibrated and ready for binding.
3. Binding
   Column Method
   1. Load the clarified sample onto the equilibrated column.
   2. Allow the sample to flow through at 0.5–1.0 mL/min.
   3. Collect the flow-through if analysis of unbound protein is desired.
   Batch Method
   1. Add equilibrated resin directly to the clarified lysate or supernatant.
   2. Incubate with gentle mixing (50–70 rpm) using a rotator or stir plate.
   3. Incubate for: 3–5 hours at room temperature, or overnight at 4°C.
   4. Transfer the resin–sample mixture to a chromatography column and allow the resin to settle.
4. Washing
   1. Wash the resin with PBS or PBS/0.09% sodium azide.
   2. Continue washing until protein in the flow-through reaches baseline levels.
   3. Monitor wash fractions using: UV absorbance at 280 nm, or Bradford protein assay.
5. Elution
   1. Elute bound IgG or protein using 0.1 M glycine, pH 2.7.
   2. Collect elution fractions (e.g., 0.5–1 mL fractions).
   3. Immediately neutralize each fraction by adding 0.1 volume of 2 M Tris-HCl, pH 8.0.
   Optional: Stepwise elution using 0.1 M citric acid buffers at pH 5.0, pH 4.0, etc. may be used for milder elution conditions. For Fc-tagged proteins, stepwise elution is recommended.
6. Analysis
   1. Analyze elution fractions using SDS-PAGE (reducing and non-reducing conditions) and size exclusion chromatography to assess aggregates.
   2. Pool fractions containing purified IgG.
   3. Dialyze or buffer exchange if necessary.
7. Resin Regeneration and Storage
   After purification:
   1. Wash with 5 column volumes of elution buffer.
   2. Re-equilibrate with 5–10 column volumes of PBS / 0.09% sodium azide.
   For deep cleaning:
   1. Wash with 2–5 CV of 6 M guanidine-HCl
   2. Wash with 2–5 CV of 0.5 M NaOH
   3. Wash with 5–10 CV deionized water
   4. Equilibrate with 5–10 CV PBS / 0.09% sodium azide or PBS / 20% ethanol
   The resin can typically be reused up to ~10 times without significant loss in binding capacity. Store at 4 °C in PBS containing 20% ethanol for long-term storage.

Tips and Tricks

• Clarify samples well - Particulates can clog columns and reduce binding efficiency. Filtration is strongly recommended for viscous samples.
• Use mild elution when possible - For sensitive antibodies or Fc-fusion proteins, stepwise citric acid elution (pH 4–5) may reduce protein aggregation.
• Collect small elution fractions – Smaller fractions improve peak resolution and help identify the most concentrated antibody fractions.
• Pre-add neutralization buffer - Place Tris neutralization buffer in collection tubes before elution to immediately protect antibodies from low-pH exposure.
• Avoid drying the resin - Dry agarose beads lose performance and may crack, reducing binding capacity.

Troubleshooting

Low IgG Recovery

• Insufficient resin volume
• Binding time too short (batch mode)
• Incorrect pH or buffer composition

• Increase resin amount
• Extend incubation time
• Ensure buffers are at neutral pH during binding

High Protein Contamination

• Insufficient washing
• Overloaded column

• Increase wash volumes
• Reduce sample load
• Add additional wash steps

Antibody Aggregation

• Exposure to low pH during elution

• Immediately neutralize fraction
• Use stepwise elution at higher pH

Slow Flow Rate

• Resin compression
• Particulate contamination

• Pre-filter samples
• Use gravity flow instead of pressure
• Reduce column packing density