Cysteine protease

Cysteine peptidase, CA clan
Crystal structure of the cysteine peptidase papain in complex with its covalent inhibitor E-64. Rendered from PDB: 1PE6​
Identifiers
Symbol	Peptidase_C1
Pfam	PF00112
Pfam clan	CL0125
InterPro	IPR000668
SMART	SM00645
PROSITE	PDOC00126
MEROPS	C1
SCOP2	1aec / SCOPe / SUPFAM
OPM superfamily	355
OPM protein	1m6d
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Cysteine proteases, also known as thiol proteases, are hydrolase enzymes that degrade proteins. These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad.^[1]

Discovered by Gopal Chunder Roy in 1873, the first cysteine protease to be isolated and characterized was papain, obtained from Carica papaya.^[1] Cysteine proteases are commonly encountered in fruits including the papaya, pineapple, fig and kiwifruit. The proportion of protease tends to be higher when the fruit is unripe. In fact, the latex of dozens of different plant families are known to contain cysteine proteases.^[2] Cysteine proteases are used as an ingredient in meat tenderizers.