Targeting a surface cavity of α1-antitrypsin to prevent conformational disease

Conformational diseases are caused by a structural rearrangement within a protein that results in aberrant intermolecular linkage and tissue deposition. This is typified by the polymers that form with the Z deficiency variant of alpha(1)-antitrypsin (Glu-342-->Lys). These polymers are retained within hepatocytes to form inclusions that are associated with hepatitis, cirrhosis, and hepatocellular carcinoma. We have assessed a surface hydrophobic cavity in alpha(1)-antitrypsin as a potential target for rational drug design in order to prevent polymer formation and the associated liver disease. The introduction of either Thr-114-->Phe or Gly-117-->Phe on strand 2 of beta-sheet A within this cavity significantly raised the melting temperature and retarded polymer formation. Conversely, Leu-100-->Phe on helix D accelerated polymer formation, but this effect was abrogated by the addition of Thr-114-->Phe. None of these mutations affected the inhibitory activity of alpha(1)-antitrypsin. The importance of these observations was underscored by the finding that the Thr-114-->Phe mutation reduced polymer formation and increased the secretion of Z alpha(1)-antitrypsin from a Xenopus oocyte expression system. Moreover cysteine mutants within the hydrophobic pocket were able to bind a range of fluorophores illustrating the accessibility of the cavity to external agents. These results demonstrate the importance of this cavity as a site for drug design to ameliorate polymerization and prevent the associated conformational disease.