Isolation of Total Proteins from Escherichia coli using SDS Lysis Method
Aim: To isolate total cellular proteins from Escherichia coli using SDS-based cell lysis method.
Principle: Bacterial cells have proteins packed inside cytoplasm. To get them out, we break the cell. Simple idea, not always simple in lab. SDS is a strong detergent, it disrupts membrane and unfolds proteins. This releases proteins into solution. Heat helps this process, makes lysis more complete. Centrifugation then removes cell debris, leaving proteins in supernatant. No fancy purification here. Just crude extract. Good enough for SDS-PAGE later. If you mix too roughly or skip steps, yield drops. I am knowing this since long, small mistakes matter more here than theory.
Requirements:
- Overnight culture of E. coli in LB broth
- LB broth medium (per 1000 ml): Tryptone 10 g/L, Yeast extract 5 g/L, NaCl 10 g/L
- Lysis buffer (per 1000 ml): Tris-HCl 50 g/L, NaCl 150 g/L, EDTA 1 g/L, SDS solution 10%,
- Distilled water
- Microcentrifuge tubes
- Micropipettes and tips
- Centrifuge
- Water bath (95°C or boiling water bath)
- Vortex mixer
- Ice box
Procedure:
- Take 1.5 ml of overnight E. coli culture in microcentrifuge tube.
- Centrifuge at 8000 rpm for 5 minutes to pellet the cells.
- Discard the supernatant carefully. Keep the pellet.
- Add 500 µl lysis buffer to the pellet. Resuspend properly.
- Add 50 µl of 10% SDS. Mix gently first, then vortex briefly.
- Keep the tube in boiling water bath for 10 minutes. Cap should be tight.
- Remove and cool on ice for 5 minutes.
- Centrifuge at 10,000 rpm for 10 minutes.
- Transfer the supernatant to a new tube. This contains proteins.
- Avoid disturbing the pellet, it looks soft sometimes.
- Store protein extract at 4°C if using same day, otherwise freeze.
Observation: After centrifugation, a clear to slightly cloudy supernatant is obtained above a compact pellet. The solution may appear viscous if protein concentration is high.
Result: Total proteins from E. coli is isolated as crude extract present in the supernatant after SDS lysis.
Conclusion: The total protein was successfully recovered from the bacterial cells using the SDS-PAGE method. This approach ensured that the proteins were concentrated while removing most of the interfering cellular debris.
Note: This protocol is for educational use in standard teaching laboratories. Small variations may occur depending on lab conditions and handling. Results may vary. biologynotes.in cannot take responsibility for any errors, misuse, or results obtained. Always follow proper lab safety and instructor guidance.