Serine proteases

Serine endopeptidases
Crystal structure of bovine chymotrypsin. The catalytic residues are shown as yellow sticks. Rendered from PDB 1CBW.
Identifiers
EC number	3.4.21.-
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Search PMC articles PubMed articles NCBI proteins

Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serine proteases fall into two broad categories based on their structure: chymotrypsin-like (trypsin-like) or subtilisin-like. In humans, they are responsible for coordinating various physiological functions, including digestion, immune response, blood coagulation and reproduction.

The MEROPS protease classification system counts 16 superfamilies (as of 2013) each containing many families. Each superfamily uses the catalytic triad or dyad in a different protein fold and so represent convergent evolution of the catalytic mechanism. The majority belong to the S1 family of the PA clan (superfamily) of proteases.

For superfamilies, P = superfamily containing a mixture of nucleophile class families, S = purely serine proteases. superfamily. Within each superfamily, families are designated by their catalytic nucleophile (S = serine proteases).

Families of Serine proteases

Serine proteases are characterised by a distinctive structure, consisting of two beta-barrel domains that converge at the catalytic active site. These enzymes can be further categorised based on their substrate specificity as either trypsin-like, chymotrypsin-like or elastase-like.