Is there any difference between the protein extraction protocol from frozen cells and cultured cells?
There shouldn't be any reason why a protein extraction protocol for living, cultured cells is different from frozen cells. However, there is a difference in handling the cells. When cells are frozen, any liquid present in the tube would form crystals and likely disrupt the cells' membrane layer. Therefore, when you thaw the frozen cells, they would not be fully intact and protein and other cellular components would be exposed in the tube (assuming the cells were not frozen with a cryoprotectant such as DMSO). Keep the thawed tube on ice until you add a lysis buffer of some kind to stabilize the proteins, avoiding protein degradation. When extracting protein from either frozen cells or fresh cells, make sure to centrifuge the cells to pellet them down and then aspirate any media or liquid before beginning extraction.
It is a good idea to freeze a cell pellet with as little liquid remaining in the tube as possible. That allows you to go directly to protein extraction without the need to remove any liquid from the pellet after thawing. Remember, any liquid in the tube after thawing would have cellular components in it and you would be removing some of your protein when you remove the liquid at this stage.
Freezing can drive water out of some LDL proteins causing them to aggregate and gel. You may have to briefly sonicate your samples if they were frozen.
While both frozen and cultured cells can be used for protein extraction, key differences exist in the protocols. Frozen cells often require additional steps, such as rapid thawing and removal of ice crystals, to preserve protein integrity. Cultured cells, on the other hand, are typically harvested with milder methods, as they are not subjected to freezing-induced stresses. Adjustments in lysis buffers and homogenization techniques may be necessary for frozen cells, ensuring efficient extraction while minimizing damage caused by the freeze-thaw process.
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