Protein C inhibitor (PCI/PROCI, also called PAI3, plasminogen activator inhibitor-3/PLANH3, plasma serine protease inhibitor) has many biological functions. It acts as a pro-coagulant in blood and in the seminal vesicles, it is required for spermatogenesis. It is a member of the clade A serpin family that includes the classical serine proteinase inhibitors, alpha-1-antitrypsin and alpha-1-antichymotrypsin, protein C inhibitor, kallistatin, and non-inhibitory serpins, like corticosteroid and thyroxin binding globulins. 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 have been associated with 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.
Comment:depending on the conformational state, the RC loop is surface accessible in the active form or buried and inserted as the central beta strand in the inactive form.
Structure:3B9F_I: Human protein C inhibitor RCL in a surface-accessible conformation
Jiyao W et al.(2023). "The conserved domain database in 2023.",