A common feature of all serine proteases is:

Serine proteases are a group of powerful enzymes that cut peptide bonds of few proteins. They help in digestion, immunity, clotting and also aid in sperm entering the egg. The active site of serine proteases contain three amino acids serine, histidine and aspaate together referred as the catalytic triad. Ref: Textbook of Biochemistry By DM Vasudevan, 3rd Edition, Page 35