The structural basis for Z α1-antitrypsin polymerization in the liver

α 1 -Antitrypsin polymers from human tissue have a structure most consistent with an intermolecular C-terminal domain swap. The serpinopathies are among a diverse set of conformational diseases that involve the aberrant self-association of proteins into ordered aggregates. α 1 -Antitrypsin deficiency is the archetypal serpinopathy and results from the formation and deposition of mutant forms of α 1 -antitrypsin as “polymer” chains in liver tissue. No detailed structural analysis has been performed of this material. Moreover, there is little information on the relevance of well-studied artificially induced polymers to these disease-associated molecules. We have isolated polymers from the liver tissue of Z α 1 -antitrypsin homozygotes (E342K) who have undergone transplantation, labeled them using a Fab fragment, and performed single-particle analysis of negative-stain electron micrographs. The data show structural equivalence between heat-induced and ex vivo polymers and that the intersubunit linkage is best explained by a carboxyl-terminal domain swap between molecules of α 1 -antitrypsin.