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IP
Sample preparation
1. To harvest cells under nondenaturing conditions, remove media and rinse cells once with ice-cold 1X PBS.
2. Remove PBS and add ice-cold 1X cell lysis buffer to each plate and incubate on the ice for 5 min.
3. Scrape cells off the plate and transfer to themicrocentrifuge tubes. Keep on the ice.
4. Sonicate on the ice three times for 5 sec each.
5. Centrifuge for 10 min at 4°C, 14,000 x g and transfer the supernatant to a new tube. If necessary, store itin -80°C.
Cell Lysate Pre-Clearing (Optional)
Pre-clearing the lysate can help reduce non-specific binding and reduce background.
1. Vortex to mix beads.
2. Add 10–30 μl of 50% Protein Aagarose bead slurry to 200 μl cell lysate at 1 mg/ml.
3. Incubate with rotation at 4°C for 30–60 min.
4. Centrifuge for 10 min at 4°C. Transfer the supernatant to a fresh tube.
5. Proceed to the next part.
Immunoprecipitation
1. Add primary antibody at the appropriate dilutionto cell lysat. Incubate with gentle agitation or rotation overnight at 4°C.
2. Add protein Aagarose(10–30 μl of 50% bead slurry). Incubate with gentle agitation or rotation for 1–3 hr at 4°C.
3. Centrifuge for 30 sec at 4°C and discard the supernatant. Wash the pellet five times with 500 μl of 1X cell lysis buffer. Keep on the ice.
4. Continue with sample analysis.
Sample Analysis
a. Western Immunoblotting
1. Resuspend the pellet with SDS sample buffer. Vortex, then centrifuge for 30 sec at 14,000 x g.
2. Heat the samples to 95–100°C for 2-5 min and centrifuge for 1 min at 14,000 x g.
3. Load the appropriate amount ofsamples on a 4–20% gel for SDS-PAGE.
4. Analyze sample by western blot.
b. Kinase Assay
1. Wash the pellet twice with 500 μl 1X kinase buffer. Keep on the ice.
2. Suspend pellet in 40 μl 1X kinase buffer supplemented with 200 μM ATP and appropriate substrate.
3. Incubate for 30 min at 30°C.
4. Terminate the reaction by adding SDS sample buffer. Vortex to mix, then centrifuge for 30 sec.
5. Transfer supernatantcontaining phosphorylated substrate to another tube.
6. Heat the sample to 95–100°C for 2–5 min and centrifuge for 1 min at 14,000 x g.Load the sample on SDS-PAGE.
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