Alpha-1-antitrypsin (also called A1AT, A1A, AAT, alpha1-proteinase inhibitor/A1PI, alpha1-antiproteinase/A1AP, proteinase inhibitor/PI, and serum trypsin inhibitor) is a protease inhibitor that belongs to the serpin superfamily. It is encoded in humans by the SERPINA1 gene. When the blood contains inadequate amounts of A1AT or functionally defective A1AT (such as in alpha-1 antitrypsin deficiency), neutrophil elastase is excessively free to break down elastin, degrading the elasticity of the lungs, which results in respiratory complications, such as chronic obstructive pulmonary disease. Normally, A1AT leaves its site of origin, the liver, and joins the systemic circulation; defective A1AT fails to do so, building up in the liver, which results in cirrhosis. This family contains other A1AT-like members of clade A of the serpin superfamily. 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:1QLP_A; Human alpha-1-antitrypsin active conformation-loop out; P1-P1' cleavage site: Met-Ser.
Structure:1IZ2_A: human alpha-1-antitrypsin, latent-uncleaved and inserted.
Jiyao W et al.(2023). "The conserved domain database in 2023.",