Affinity purification

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Before you begin, you will need at least 1mg of protein (eg.GST-FAA-N) and at least 1mg of ‘clearing’ protein (probably GST). This means that you will probably need 2 columns and twice as much reagent. The clearing protein will be used to make its own column in the exact same way as the fusion protein column. If you are using peptide for this column you will skip step A.

  1. Buffer exchange
    • Dilute ligand (eg. FAA-N-GST) 1:10 in pH 10 Coupling Buffer. Reconcentrate to 1ml in 50mL 10Kmwco Centricon
    • Make 1:3mL dilution of exchanged sample. This is the Ligand Solution.
  2. make slurry
    • Put 2-5mL of Coupling Gel into a 14mL conical centrifuge tube.
    • Wash w/ 5mL Coupling Buffer pH 10. Centrifuge for 5-10minutes at 1000xg. Aspirate supernate carefully.
    • Add Ligand Solution. Rock for 4hours at 4∞C.
  3. Immobilize ligand
    • Centrifuge Coupling Gel (5-10 minutes at 1000xg) and remove ligands solution.
    • Wash coupling gel w/5mL of coupling buffer pH7.2.
    • Make up 5M Cyanoborohydride solution. (.0785g/250µL dH20). Make solution in the hood and make the solution fresh each time you use it. Check and make sure the solution is white or whitish-yellow (Sigma).
    • Combine 2mL Coupling Buffer pH7.2 and 40µL of 5M Cyanoborohydride. Rock overnight at room temperature.
  4. Quenching buffer
    • Centrifuge Coupling Gel and remove remaining liquid. Dispose of all Cyanoborohydride as Hazardous waste.
    • Wash slurry w/ 4mL Quenching Buffer (1M Tris-HCl pH 7.4).
    • Add 2mL Quenching Buffer and 40µL 5M Cyanoborohydride.
    • Rock end over end for 30 minutes.
  5. FInal washing and column assembly
    • Centrifuge Coupling Gel and remove Quenching Buffer. Dispose of all Cyanoborohydride as Hazardous waste.
    • Wash 4x5mL with 1M NaCl.
    • Wash 2x5mL with degassed dH20.
    • Assemble column (stop bottom and add 2mL water, float filter disk on top and push down to bottom of column, let water drain out of column)
    • Add slurry to column and let settle for 45minutes.
    • After slurry settles, add top filter disk and push down close (2mm) to coupling gel.
    • Remove bottom cap and let drain.
    • Wash Column with 8mL 1x PBS
  6. Serum incubation
    • Dilute Serum 1:1 with 1xPBS
    • Run Serum through “clearing column” (GST only) 3-4 times, collecting FT.
    • Run Serum (FT) through the Affinity column (eg FAA-N GST) 3-5 times.
    • Wash the column with 8mL 1x PBS to get rid of weak binding.
    • Elute w/ 8x 1mL of 2.8pH 0.1M Glycine. Neutralize samples with 50µL of 1M Tris pH 9.5
    • Reactivate column w/16mL 1M NaCl and 8mL degassed dH20 within 1/2 hour.
    • Store in degassed dH20 and .05% NaAzide.
  7. Protein concentration
    • UV spec samples at 280nm against a 0.1M Glycine pH2.8 + 50µL 1M Tris pH 9.5 blank.
    • Combine samples with significant readings, aliquot and store in -20.
    • Make sure pH of samples is ~pH8.
    • Store in .05% NaAzide.
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