Serpin (nonfiction)
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Serpins are a superfamily of proteins, notable for their irreversible protease inhibition of target proteases.
Mechanism of action
Serins 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.
Found in all kingdoms of life
Serpins are found in all kingdoms of life.
Name
The acronym serpin was originally coined because the first serpins to be identified act on chymotrypsin-like serine proteases (serine protease inhibitors).
Biological processes
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.
Similar structures
Although most serpins control proteolytic cascades, some proteins with a serpin 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 serpin is used to describe these members as well, despite their non-inhibitory function, since they are evolutionarily related.