Identification of a 4-mer Peptide Inhibitor that Effectively Blocks the Polymerization of Pathogenic Z α₁-Antitrypsin

Abstract

alpha(1)-Antitrypsin (AT) is a major proteinase inhibitor within the lung. The Z variant of AT (E342K) polymerizes within the liver and lung, resulting in hepatic aggregation of AT and tissue deficiency, predisposing to early onset of cirrhosis and emphysema, respectively. Polymerization of the aberrant protein can be prevented in vitro by specific peptides such as FLEAIG. This peptide serves as a lead molecule to design a shorter peptide that may be effective as a therapeutic agent. In this study we employed a systematic chemical approach using alanine scanning of Ac-FLEAIG-OH and subsequent peptide shortening to study the binding of shorter peptides to Z-AT. While two additional 6-mer peptides Ac-FLAAIG-OH and Ac-FLEAAG-OH were found to bind to Z-AT, their daughter peptides Ac-FLEAA-NH(2) and Ac-FLAA-NH(2) also bound avidly to Z-AT and prevented polymerization of the protein. Further comparative studies revealed that the binding of Ac-FLAA-NH(2) was more specific for Z-AT. The peptide-AT complex formation was enhanced by the presence of C-terminal amide group on the peptide, and circular dichroism analysis demonstrated that a random coil rather than a beta-helical conformation favored binding of the peptide to AT. In summary, this study has identified novel small peptides that inhibit Z-AT polymerization, and are a significant advance towards the treatment of Z-AT-related cirrhosis and emphysema.

Recent advances in α-1-antitrypsin deficiency-related lung disease

“…The resulting polymers lead to aggregation in hepatocytes and subsequent plasma deficiency [25]. A strategy to try and prevent polymerization has been the use of small peptides to compete with reactive loops and bind to β-sheet A [125][126][127][128][129]. Although in vitro tests are promising, challenges to this approach being translated to humans have included how to deliver the peptides to the ER of hepatocytes and the fact that they inactivate Z A1AT [127], therefore potentially worsening plasma deficiency, emphysema risk and progression.…”

Polymerization and Oxidation of Alpha-1-Antitrypsin in Pathogenesis of Emphysema

“…This approach could potentially ameliorate the liver disease, and defend respiratory epithelial surface, providing antielastase protection and avoiding the proinflammatory effects of polymerized Z A1AT. Currently, there is some progress in development of synthetic peptide designed to selectively inhibit Z polymerisation Parfrey et al, 2004;Chang et al, 2006;Mallya et al, 2007;Chang et al, 2009). …”

The Role of Alpha-1 Antitrypsin in Emphysema

“…These methods reduce intracellular aggregation of Z-AT but do not increase the secretion Z-AT. Use of short synthetic peptides targeting -sheet A may show therapeutic potential for Z-AT related liver and lung disease (Figure 3) (Chang et al, 2006; Unpublished observation).…”