<unk> s 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<unk>  was originally coined because the first<unk> s to be identified act on chymotrypsin-like<unk> e proteases <unk> e 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 the target's 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<unk> s 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:<unk> s are vulnerable to mutations that can result in<unk> opathies such as protein misfolding and the formation of inactive long-chain polymers.<unk>  polymerisation not only reduces the amount of active inhibitor, but also leads to accumulation of the polymers, causing cell death and organ failure. Although most<unk> s control proteolytic cascades, some proteins with a<unk>  structure are not enzyme inhibitors, but instead perform diverse functions such as storage (as in egg white—ovalbumin), transport as in hormone carriage proteins (thyroxine-binding globulin, cortisol-binding globulin) and molecular chaperoning (HSP47). The term<unk>  is used to describe these members as well, despite their non-inhibitory function, since they are evolutionarily related.
Serpin
Thrombin
Immunoevasin
Kallikrein
Plasminogen 
Hemostat
Anordrin
Tetanospasmin