Cathepsin

Cathepsin
Structure of Cathepsin K
Identifiers
Symbol	CTP
Pfam	PF00112
Pfam clan	CL0125
InterPro	IPR000668
SMART	Pept_C1
PROSITE	PDOC00126
MEROPS	C1
SCOP2	1aec / SCOPe / SUPFAM
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Cathepsins (Ancient Greek kata- "down" and hepsein "boil"; abbreviated CTS) are proteases (enzymes that degrade proteins) found in all animals as well as other organisms. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave^{[citation needed]}. Most of the members become activated at the low pH found in lysosomes. Thus, the activity of this family lies almost entirely within those organelles. There are, however, exceptions such as cathepsin K, which works extracellularly after secretion by osteoclasts in bone resorption. Cathepsins have a vital role in mammalian cellular turnover.