protein storage?

Question

Dear, I want to store proteins. Is it better to store my proteins (IgM) under 4 celsius degree or -20 celsius degree? Is there any way to improve the proteins' stablity in solution for preservation?

Answer 1

-- General Proteins --

Temperature:
Generally, proteins are best stored at ≤ 4°C in clean, autoclaved glassware or polypropylene tubes. Storage at room temperature often leads to protein degradation and/or inactivity, commonly as a result of microbial growth. For short term storage (1 day to a few weeks), many proteins may be stored in simple buffers at 4°C.
For long term storage for 1 month to 1 year, some researchers choose to bead single-use aliquots of the protein in liquid nitrogen for storage in clean plastic containers under liquid nitrogen. This method involves adding the protein solution dropwise (about 100 µl each) into a pool of liquid nitrogen, then collecting the crop-sized frozen beads and storing them in cryovials under liquid nitrogen. Frozen at -20°C or -80°C is the more common form of cold protein storage. Because freeze-thaw cycles decrease protein stability, samples for frozen storage are best dispensed and prepared in single-use aliquots so that, once thawed, the protein solution will not have to be refrozen. Alternatively, addition of 50% glycerol or ethylene glycol will prevent solutions from freezing at -20°C, enabling repeated use from a single stock without warming (i.e., thawing).

Protein Concentration:
Dilute protein solutions (< 1 mg/ml) are more prone to inactivation and loss as a result of low-level binding to the storage vessel. Therefore, it is common practice to add “carrier” or “filler” protein, such as purified bovine serum albumin (BSA) to
1-5 mg/ml (0.1-0.5%), to dilute protein solutions to protect against such degradation and loss.

Additives:
Many compounds may be added to protein solutions to lengthen shelf life:
• Protein Stabilizing Cocktail is a 4X solution that helps to extend the shelf-life of most proteins for storage at 4°C or -20°C.
• Cryoprotectants such as glycerol or ethylene glycol to a final concentration of 25-50% help to stabilize proteins by preventing the formation of ice crystals at -20°C that destroy protein structure.
• Protease inhibitors prevent proteolytic cleavage of proteins
• Anti-microbial agents such as sodium azide (NaN3) at a final concentration of 0.02-0.05% (w/v) or thimerosal at a final concentration of 0.01 % (w/v) inhibit microbial growth.
• Metal chelators such as EDTA at a final concentration of 1-5 mM avoid metal-induced oxidation of –SH groups and helps to maintain the protein in a reduced state.
• Reducing agents such a dithiothreitol (DTT) and 2-mercaptoethanol (2-ME) at final concentrations of 1-5 mM also help to maintain the protein in the reduced state by preventingoxidation of cysteines.

-- Storage Conditions for Antibodies and Antibody-Enzyme Conjugates --

Antibody stock solutions (e.g., 1 mg/ml) often may be stored at 4°C for days to weeks without significant loss in activity. For increased stability, glycerol or ethylene glycol may be added to a final concentration of 50% and the antibody stored at -20°C. Alternatively, the antibody solution may be stored in small working aliquots at -20°C to avoid repeated freeze-thaw cycles. Anti-microbial agents such as sodium azide or thimerosal may be added to avoid microbial growth.
Generally, antibody conjugates are best stored at -20°C with glycerol or ethylene glycol added at a final concentration of 50%. Although some enzyme conjugates may be stored at -20°C without cryoprotectant, frozen stocks must be as single usealiquots to prevent repeated freeze-thaw cycles; alkaline phosphatase conjugates are particularly sensitive to freezing.
Conjugates typically maintain good activity for 1-2 years if stored at -20°C with glycerol or ethylene glycol. However, contaminants in cryoprotectants may affect enzyme activity, and few researchers take steps to ensure the purity of the cryoprotectant used. Ethylene glycol does not support microbial growth, making it preferable to glycerol.

Answer 2

Aurora's answer is very detailed and covers pretty much everything.

However some antibodies cannot withstand even one thawing without denaturing.
If you bought it, contact the supplier.
Keeping it in 50% glycerol in small aliquots at -20 is what I usually do unless otherwise noted by the supplier.
If you can freeze it, you can keep a tube with enough to make a new batch of aliquots at -80. But then again this is for using antibodies in assays like western blotting and not a general rule for storing expressed proteins; that would also depend on the experiments you are planning to do with it since some additives could interfere with your experiment.

Answer 3

Proteins will remain stable for a much longer period of time at -20 degrees C.
Sodium Chloride can be used to help prevent the decomposition of proteins.