Cleaved antitrypsin polymers at atomic resolution

α₁-Antitrypsin deficiency, which can lead to both emphysema and liver disease, is a result of the accumulation of α₁-antitrypsin polymers within the hepatocyte. A wealth of biochemical and biophysical data suggests that α₁-antitrypsin polymers form via insertion of residues from the reactive center loop of one molecule into the β-sheet of another. However, this long- standing hypothesis has not been confirmed by direct structural evidence. Here, we describe the first crystallographic evidence of a β-strand linked polymer form of α₁-antitrypsin: the crystal structure of a cleaved α₁- antitrypsin polymer.