Protease, also called proteinase, peptidase, or proteolytic enzyme, is any enzyme that performs proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in a polypeptide chain. Proteases have evolved to perform these reactions by numerous different mechanisms. Proteases have evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms. Protease can be found in animals, plants, fungi, bacteria, archaea and viruses, highlighting the important role that they play in all forms of life on Earth. Proteases are involved in protein processing, regulation of protein function, apoptosis, viral pathogenesis, digestion, photosynthesis, and numerous other vital processes.
Protease can be classified into seven broad groups:
Serine proteases - using a serine alcohol, display a wide range of functions.
Cysteine proteases - using a cysteine thiol, that include caspases which are involved in apoptosis and inflammation, and cathepsins which promote protein degradation.
Threonine proteases - using a threonine secondary alcohol
Aspartic proteases - using an aspartate carboxylic acid, that include beta and gamma secretases, the two enzymes necessary to release amyloid beta peptides from the Alzheimer's disease associated amyloid precursor protein (APP).
Glutamic proteases - using a glutamate carboxylic acid
Metalloproteases - using a metal, usually zinc. The Metalloprotease family includes aminopeptidases and endopeptidases, which are secreted, membrane-bound, or cytosolic.