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serpin B family, ov-serpins The clade B of the serpin superfamily corresponds to the ovalbumin family of serpins (ov-serpins), a family of closely related proteins, whose members can be secreted (ovalbumin), cytosolic (leukocyte elastase inhibitor, LEI), or targeted to both compartments (plasminogen activator inhibitor 2, PAI-2). Family members are also characterized by N- and C-terminal extensions, the absence of a signal peptide, and a Ser rather than an Asn residue at the penultimate position. In general, SERine Proteinase INhibitors (serpins) exhibit conformational polymorphism shifting from native to cleaved, latent, delta, or polymorphic forms. Many serpins, such as antitrypsin and antichymotrypsin, function as serine protease inhibitors which regulate blood coagulation cascades. Non-inhibitory serpins perform many diverse functions such as chaperoning proteins or transporting hormones. Serpins are of medical interest because mutants can cause blood clotting disorders, emphysema, cirrhosis, and dementia. A classification based on evolutionary relatedness has resulted in the assignment of serpins to 16 clades designated A-P along with some orphans.
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