Serpins (serine protease inhibitors) are the largest and most broadly distributed superfamily of protease inhibitors. The majority of serpins inhibit serine proteases, but serpins that inhibit caspases and papain-like cysteine proteases have also been identified. Serpins irreversibly inhibit their target protease by undergoing a large conformational change to disrupt its active site.
Serpins are an important family of proteinase inhibitors present in higher eukaryotes. Numerous human serpins have been implicated in disease processes such as heart disease, cancer, liver cirrhosis and emphysema. Serpins are able to undergo a massive conformational rearrangement, which is essential for their mechanism of inhibition. Many disease-linked mutations in serpins occur in regions of the molecule central to the conformational change and result in instability and polymerisation.