The superfamily of high molecular weight serine proteinase inhibitors (serpins) regulate a diverse set of intracellular and extracellular processes such as complement activation, fibrinolysis, coagulation, cellular differentiation, tumor suppression, apoptosis, and cell migration. Serpins are characterized by well-conserved a tertiary structure that consists of 3 beta sheets and 8 or 9 alpha helices (Huber and Carrell, 1989 [PubMed 2690952]). A critical portion of the molecule, the reactive center loop connects beta sheets A and C. Protease inhibitor-8 (PI8; SERPINB8) is a member of the ov-serpin subfamily, which, relative to the archetypal serpin PI1 (MIM 107400), is characterized by a high degree of homology to chicken ovalbumin, lack of N- and C-terminal extensions, absence of a signal peptide, and a serine rather than an asparagine residue at the penultimate position