The discovery of proteases and intramembrane proteolysis .

Proteases carry out a wide variety of physiological functions. This review presents a brief history of protease research, starting with the original discovery of pepsin in 1836. Following the path of time, we revisit how proteases were originally classified based on their catalytic mechanism and how chemical and crystallographic studies unravelled the mechanism of serine proteases. Ongoing research on proteases addresses their biological roles, small molecule inhibitors for therapeutic uses, and protein engineering to modify their activities. The discovery of intramembrane proteases is more recent, beginning with the discovery of site-2 protease in 1997. Since then, different mechanistic classes of intramembrane proteases have been characterized, and many of these act in regulated intramembrane proteolysis in signaling pathways. Furthermore, the rhomboid intramembrane proteases were discovered by genetic and biochemical experiments in and then in human cells. Research on the intramembrane proteases is expanding, as their biological importance is recognized.