Knight:NuPAGE electrophoresis

For a much cheaper version of this protocol, see Sauer:bis-Tris SDS-PAGE, the very best.

Purpose

To run a denaturing protein gel. Note that a preferable version of this protocol is available at Sauer:bis-Tris SDS-PAGE, the very best (recommended by Kathleen). But since we seem to already have the Invitrogen kit contents in lab, this protocol describes use of the Invitrogen system.

Materials

• NuPAGE Novex 10% Bis-Tris Gel 1.0 mm, 10 well (for small proteins e.g. 13kD) or NuPAGE Novex 4-12% Bis-Tris Gel 1.0 mm, 10 well (for medium proteins e.g. 50-60kD)
• XCell SureLock Mini-Cell electrophoresis apparatus
• 20X MES or MOPS Running Buffer
• NuPAGE LDS Sample Buffer (4X)
• NuPAGE Reducing Agent (10X)
• NuPAGE Antioxidant
• SeeBlue Plus2 Pre-Stained Standard
• Invitrogen SimplyBlue SafeStain

Procedure

Running buffer preparation

Do this step first.

1. Prepare 1000mL 1X NuPAGE SDS running buffer
   • 50mL 20X MES Running Buffer (for very small proteins e.g. 13kD) or 20X MOPS Running Buffer (for medium-sized proteins e.g. 50-60kD).
   • 950mL deionized water
2. Mix well.
3. Set aside 200mL buffer for use in Upper (Inner) buffer chamber).
   • Add 500μL NuPAGE Antioxidant immediately before running the gel.
   • Mix well.

Sample preparation

1. Wells can accommodate 25μL loading volume.
   • Likely they can accommodate more ... maybe 40μL.
2. Let sample buffer warm to room temperature.
3. Each sample should contain
   • 13 μL protein sample (max 0.5μg per band)
   • 5 μL NuPAGE LDS Sample Buffer
   • 2 μL NuPAGE Reducing Agent
4. Heat samples at 70°C for 10 mins.

Set up the gel apparatus during the 10 mins sample heating step.

Note that prestained molecular weight marker doesn't need any preparation.

Running the gel

1. Wear gloves.
2. Remove the NuPAGE gel from the pouch.
3. Rinse the gel cassette with deionized water.
4. Peel the tape from the bottom of the cassette.
5. Gently pull the comb from the cassette in one smooth motion.
6. Rinse the sample wells with 1X NuPAGE SDS running buffer.
   • Use a pipetman and pipet to squirt in running buffer.
7. Invert and shake to remove buffer.
8. Repeat rinse two more times.
9. Orient the two gels in the Mini-Cell such that the notched "well" side of the cassette faces inward towards the buffer core.
10. Seat the gels on the bottom of the Mini-Cell and lock into place with the gel tension wedge.
    • Use the plastic buffer dam if you are only running one gel.
11. Fill the upper buffer chamber with a small amount of upper buffer chamber running buffer (with antioxidant) to check tightness of seal.
    • If there is a leak, discard buffer, reseal chamber and try again.
12. Fill upper buffer chamber. Buffer level should exceed level of the wells. Requires about 200mL
13. Load samples.
14. Load protein molecular weight marker (20 μL per lane but 10μL also seems to work).
15. Fill lower buffer chamber at the gap near locking mechanism with 600mL NuPAGE SDS running buffer.
16. Run at 200V for 30 minutes.

Staining the gel

1. Shut off the power.
2. Disconnect electrodes.
3. Remove gels.
4. Insert a knife in between the two plates and pry the plates apart.
   • You should hear a cracking noise as you break the bond between the two plates.
5. Gently separate the two plates attempting to leave the gel on the bottom slotted plate.
6. Cut to separate gel from bottom lip.
7. Flip over and transfer gel to staining tray that has been prefilled with 100mL deionized water (see below).
   • Use lid of a 1000μL pipette tip box.

You have three options for staining at this point.

1. Knight:NuPAGE electrophoresis/Fast staining (fast but less sensitive protocol)
2. Knight:NuPAGE electrophoresis/Slow staining (slow but more sensitive protocol)
3. Knight:NuPAGE electrophoresis/Hybrid staining (allows you to see results immediately but take gel picture when the gel is stained more thoroughly)

See Knight:NuPAGE electrophoresis/Gel drying for instructions on how to dry and preserve the gel.

Notes

• To date, the best staining tray I've found is the lid of a 1000μL pipette tip box. Then use a piece of mesh that just fits inside the lide to either keep the gel in place while changing solutions or to move the gel to and from the light box. This method requires smaller volumes of stain than the staining tray from Invitrogen.
• There are several ways to screw up this protocol, I list them here in the hopes that it may help people avoid these trivial mistakes.
  1. The inner and outer chambers of running buffer are not sealed from one another.
  2. Reverse the electrodes in the power supply.
  3. Putting the gel in backwards in the apparatus.

Safety

• Use nitrile gloves when handling acrylamide.
• Dispose of acrylamide gels and trays as hazardous.

See here for detailed safety information.

References

1. NuPAGE Technical Guide