[A1AT_HUMAN] Defects in SERPINA1 are the cause of alpha-1-antitrypsin deficiency (A1ATD) [MIM:613490]. A disorder whose most common manifestation is emphysema, which becomes evident by the third to fourth decade. A less common manifestation of the deficiency is liver disease, which occurs in children and adults, and may result in cirrhosis and liver failure. Environmental factors, particularly cigarette smoking, greatly increase the risk of emphysema at an earlier age.  
[A1AT_HUMAN] Inhibitor of serine proteases. Its primary target is elastase, but it also has a moderate affinity for plasmin and thrombin. Irreversibly inhibits trypsin, chymotrypsin and plasminogen activator. The aberrant form inhibits insulin-induced NO synthesis in platelets, decreases coagulation time and has proteolytic activity against insulin and plasmin.[:]  Short peptide from AAT: reversible chymotrypsin inhibitor. It also inhibits elastase, but not trypsin. Its major physiological function is the protection of the lower respiratory tract against proteolytic destruction by human leukocyte elastase (HLE).[:] 
Publication Abstract from PubMed
The crystal structure of a recombinant human alpha 1-antitrypsin, in the uncleaved and uncomplexed state, has been determined by X-ray crystallographic methods and refined to an R-factor of 18.4% for 8.0-3.46 A data with good stereochemistry. This structure provides the first view at the inhibitory loop and the central beta-sheet A of the uncleaved alpha 1-antitrypsin. The reactive loop takes a distorted helical conformation and no pre-insertion of two residues in the reactive loop into the beta-sheet A is observed. The present structure is largely in agreement with the model predicted by Engh, Wright, and Huber [Prot. Eng. 3 (1990) 469-477].
Crystal structure of an uncleaved alpha 1-antitrypsin reveals the conformation of its inhibitory reactive loop.,Song HK, Lee KN, Kwon KS, Yu MH, Suh SW FEBS Lett. 1995 Dec 18;377(2):150-4. PMID:8543039
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.