Aggregation of plasma Z type alpha 1-antitrypsin suggests basic defect for the deficiency

The abnormal type of alpha 1-antitrypsin, PI (protease inhibitor) type Z, is associated with inclusion bodies in the liver, which contain non-secreted alpha 1-antitrypsin. Our studies show that Z protein has an inherent tendency to aggregate, even in plasma. Depending upon conditions, from 15 to 70% of the Z protein in plasma was in a high-Mr form, compared with 1.5% of M type alpha 1-antitrypsin. The high-Mr complex in plasma cannot be disaggregated using Triton X detergent or reducing conditions. This increased tendency to aggregate can be explained by the mutation affecting, tertiary structure and salt bridge formation in Z protein. We have observed this same tendency to aggregate for Mmalton alpha 1-antitrypsin, a rarer variant also associated with a plasma deficiency.