serpin family G member 1, plasma proteinase C1 inhibitor
Plasma proteinase C1 inhibitor (C1-INH/C1IN) is a protease inhibitor of the serpin family. It plays a pivotal role in regulating the activation of the classical complement pathway and of the contact system, via regulating bradykinin formation, inhibiting factor XII and kallikrein of the contact system, and via acting on factor XI in the coagulation cascade. This subgroup corresponds to clade G of the serpin superfamily. 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:5DU3_A: Human C1-inhibitor, active form, open RCL
Structure:2OAY_A: Human C1-inhibitor, latent form, RCL inserted into beta sheet
Jiyao W et al.(2023). "The conserved domain database in 2023.",