Serpin

Serpin (serine protease inhibitor)
A serpin (white) with its 'reactive centre loop' (blue) bound to a protease (grey). Once the protease attempts catalysis it will be irreversibly inhibited. (PDB: 1K9O​)
Identifiers
Symbol	Serpin, SERPIN (root symbol of family)
Pfam	PF00079
InterPro	IPR000215
PROSITE	PDOC00256
SCOP	1hle
SUPERFAMILY	1hle
CDD	cd00172
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be identified act on chymotrypsin-like serine proteases (serine protease inhibitors). They are notable for their unusual mechanism of action, in which they irreversibly inhibit their target protease by undergoing a large conformational change to disrupt its active site. This contrasts with the more common competitive mechanism for protease inhibitors that bind to and block access to the protease active site.

Protease inhibition by serpins controls an array of biological processes, including coagulation and inflammation, and consequently these proteins are the target of medical research. Their unique conformational change also makes them of interest to the structural biology and protein folding research communities. The conformational-change mechanism confers certain advantages, but it also has drawbacks: serpins are vulnerable to mutations that can result in serpinopathies such as protein misfolding and the formation of inactive long-chain polymers. Serpin polymerisation not only reduces the amount of active inhibitor, but also leads to accumulation of the polymers, causing cell death and organ failure.