Will anything happen to my protein if the cells have been stored in the -20 freezer for more than a month?

Question

Basically I grew up a mutant protein in E. Coli BL21 cells on the 4th of July and I'm only extracting and purifying the protein now (the 13th of August). The cells were stored in the -20 degree freezer in pellet form all this time. If my protein does indeed have activity, would the activity have been significantly affected due to storing it in this way for this long?

Thank you.

Answer 1

It is very individual for different proteins. Mostly, storage in frozen cells is OK. I prefer to store pellet at -80. But situation with purified protein is more difficult. Some protein you can store at -20 in 50% glycerol (antifreeze and stabilizing agent at the same time). Some proteins can be flash friezed in liquid N2 and stored at -80. But for any exact protein it should be proved experimentally.

Answer 2

They should be fine. I've isolated proteins from samples stored for several months at -20C and used them for Western blots. Avoid repeated freeze thaw cycles. I always prepare allaquots for single reactions and freeze individually. In the furure you may want to consider using a -80 ultralow if you have access to one.

The link below is to a good Technical Resource on protein storage.