6-mer Peptide Selectively Anneals to a Pathogenic Serpin Conformation and Blocks Polymerization

Conformational diseases such as amyloidosis, Alzheimer's disease, prion diseases, and the serpinopathies are all caused by structural rearrangements within a protein that transform it into a pathological species. These diseases are typified by the Z variant of α1-antitrypsin (E342K), which causes the retention of protein within hepatocytes as inclusion bodies that are associated with neonatal hepatitis and cirrhosis. The inclusion bodies result from the Z mutation perturbing the conformation of the protein, which facilitates a sequential interaction between the reactive center loop of one molecule and β-sheet A of a second. Therapies to prevent liver disease must block this reactive loop-β-sheet polymerization without interfering with other proteins of similar tertiary structure. We have used reactive loop peptides to explore the differences between the pathogenic Z and normal M α1-antitrypsin. The results show that the reactive loop is likely to be partially inserted into β-sheet A in Z α1-antitrypsin. This conformational difference from M α1-antitrypsin was exploited with a 6-mer reactive loop peptide (FLEAIG) that selectively and stably bound Z α1-antitrypsin. The importance of this finding is that the peptide prevented the polymerization of Z α1-antitrypsin and did not significantly anneal to other proteins (such as antithrombin, α1-antichymotrypsin, and plasminogen activator inhibitor-1) with a similar tertiary structure. These findings provide a lead compound for the development of small molecule inhibitors that can be used to treat patients with Z α1-antitrypsin deficiency. Furthermore they demonstrate how a conformational disease process can be selectively inhibited with a small peptide.