Binding biotinylated nucleic acids, antibodies, or proteins to Hydrophilic Streptavidin Magnetic Beads (NEB #S1421) for Pull-Down experiments

Materials:

  NEB Product
Hydrophilic Streptavidin Magnetic Beads S1421S
Magnetic rack sized appropriately for your experiment  
        96-well Microtiter Plate Magnetic Separation Rack S1511S
        6-tube Magnetic Separation Rack for 1.5 mL microfuge tubes S1506S
        12-tube Magnetic Separation Rack for 1.5 mL microfuge tubes S1509S
        50 mL Magnetic Separation Rack for 50 mL conical tubes S1507S

Biotinylated bait (nucleic acid, antibody or protein)

Binding/Wash buffer for nucleic acids: 10 mM Tris-HCl pH 7.5, 1 M NaCl, 1 mM EDTA

Binding/Wash buffer for antibodies or proteins: 1X PBS pH 7.4 (+ 0.01% w/v BSA and/or 0.05% Tween-20 to reduce non-specific binding)

Optional: NanoDrop/spectrophotometer

 

 

Protocol:

  1. Vortex/mix the tube containing the Hydrophilic Streptavidin Magnetic Beads to fully resuspend them.
  2. Transfer the required volume of beads for your experiment to a sterile tube. Hydrophilic Streptavidin Magnetic Beads bind 400 pmol of 25 bp single stranded DNA (ssDNA) or 30 ug of biotinylated antibody or protein per milligram of beads; the beads are supplied at 4 mg/mL.

    1. Note: Optimal loading density of biotinylated bait on beads needs to be determined empirically.  We recommend these values as a starting point.

  3. Place the tube in the magnetic rack and allow the beads to pellet; remove the storage buffer.
  4. Remove the tube from the magnetic rack. Equilibrate the beads with appropriate binding/wash buffer by mixing the beads thoroughly in a volume of binding buffer equal to or greater than the volume of beads transferred in step 2.
  5. Place the tube in the magnetic rack and allow the beads to pellet. Remove the binding/wash buffer.
  6. Repeat steps 4 and 5 twice more for a total of 3 equilibration washes.
  7. Resuspend the biotinylated bait in appropriate binding buffer (adjusting the NaCl concentration of this solution to be between 0.5 and 1 M after resuspension for biotinylated nucleic acid baits)

    1. Optional: Measure the A260 (nucleic acid) or A280 (antibody/protein) of the resuspended biotinylated bait to determine amount of target bound

  8. Add the resuspended biotinylated bait to pelleted and equilibrated magnetic beads. Mix thoroughly by pipet mixing or gentle vortexing.
  9. Incubate with mixing (rotisserie-style end-over-end mixing or ThermoMixer/equivalent) for > 30 minutes at room temperature or 4°C, depending on the stability of your biotinylated bait.
  10. Place the tube in the magnetic rack and allow the beads to pellet.

    1. Optional: Measure the A260 or A280 of the solution to quantify how much biotinylated bait remains. The difference between the first measurement and this measurement is a good approximation of the amount of biotinylated bait bound to the Streptavidin Magnetic Beads

  11. Wash the beads with the appropriate binding/washing buffer (or a wash buffer of higher stringency) as in steps 4-6.
  12. Resuspend the beads in a buffer compatible with your specific pull-down experiment; proceed directly to the pull-down experiment.