The Protein Man's Blog | A Discussion of Protein Research

 In a cell, protein degradation and synthesis maintain the balance of proteins, where old proteins are degraded into amino acids, which are further used in the synthesis of new proteins. Proteases/Peptidases play an important role in protein degradation. Proteases are present in almost all living cells. In a living cell, protease action is regulated by external as well as internal factors. Some proteases are inactive under normal conditions, but are activated only when necessary. For example, during apoptosis, Pro-caspase (inactive) converts to Caspase (active). Sub-cellular localization of proteases also helps in their regulated activity. Most of them are localized to sub-cellular organelles like lysosomes and thereby restricted their activity only to those proteins directed to lysosomes. 

What is a Protease Inhibitor?

If you want to protect your target protein from potential harm, there is one thing you should do – use a protease inhibitor.

Proteins are phosphorylated and dephosphorylated all the times in the cells in a highly regulated manner. Protein phosphorylation and dephosphorylation are critical for signaling, cell division, protein translation, metabolism and survival. Activity of substrate proteins is tightly regulated by concerted activities of kinases and phosphatases in-vivo. On an average, roughly 3% of a typical eukaryotic genome encodes for kinases or phosphatases, yet more than 30% of the total number of proteins in a cell undergoes phosphorylation. As previously discussed, there is no general rule about effect of phosphorylation on proteins and same is true for dephosphorylation also. The effect of phosphorylation or dephosphorylation varies in context with different proteins.

While proteases are essential in maintaining the proper function of living cells, researchers often do not welcome their presence in their protein samples. Why would they when the mere presence of these enzymes jeopardizes the integrity of their samples and puts them one step closer to imminent degradation? No researcher would be happy knowing that there are proteases in their samples, just waiting to chew up on their precious protein, especially if their target protein is low in abundance.