The Z mutant of α 1 -antitrypsin (Glu342Lys) causes a domain-swap and the formation of intrahepatic polymers that aggregate as inclusions and predispose the homozygote to cirrhosis. We have identified an allosteric cavity that is distinct from the interface involved in polymerisation for rational structurebased drug design to block polymer formation. Virtual ligand screening was performed on 1.2 million small molecules and 6 compounds were identified that reduced polymer formation in vitro. Modelling the effects of ligand binding on the cavity and re-screening the library identified an additional 10 compounds that completely blocked polymerisation. The best antagonists were effective at ratios of compound to Z α 1 -antitrypsin of 2.5:1 and reduced the intracellular accumulation of Z α 1 -antitrypsin by 70% in a cell model of disease. Identifying small molecules provides a novel therapy for the treatment of liver disease associated with the Z allele of α 1 -antitrypsin.

The common Z mutant (Glu342Lys) of α1-antitrypsin results in the formation of polymers that are retained within hepatocytes. This causes liver disease whilst the plasma deficiency of an important proteinase inhibitor predisposes to emphysema. The Thr114Phe and Gly117Phe mutations border a surface cavity identified as a target for rational drug design. These mutations preserve inhibitory activity but reduce the polymerisation of wild-type native α1-antitrypsin in vitro and increase secretion in a Xenopus oocyte model of disease. To understand these effects, we have crystallised both mutants and solved their structures. The 2.2 Å structure of Thr114Phe α1-antitrypsin demonstrates that the effects of the mutation are mediated entirely by well-defined partial cavity blockade and allows in silico screening of fragments capable of mimicking the effects of the mutation. The Gly117Phe mutation operates differently, repacking aromatic side chains in the helix F–β-sheet A interface to induce a half-turn downward shift of the adjacent F helix. We have further characterised the effects of these two mutations in combination with the Z mutation in a eukaryotic cell model of disease. Both mutations increase the secretion of Z α1-antitrypsin in the native conformation, but the double mutants remain more polymerogenic than the wild-type (M) protein. Taken together, these data support different mechanisms by which the Thr114Phe and Gly117Phe mutations stabilise the native fold of α1-antitrypsin and increase secretion of monomeric protein in cell models of disease.

Members of the serine proteinase inhibitor or serpin superfamily inhibit their target proteinases by a remarkable conformational transition that involves the enzyme being translocated more than 70 A (1 A = 10(-10) m) from the upper to the lower pole of the inhibitor. This elegant mechanism is subverted by point mutations to form ordered polymers that are retained within the endoplasmic reticulum of secretory cells. The accumulation of polymers underlies the retention of mutants of alpha(1)-antitrypsin and neuroserpin within hepatocytes and neurons to cause cirrhosis and dementia respectively. The formation of polymers results in the failure to secrete mutants of other members of the serpin superfamily: antithrombin, C1 inhibitor and alpha1-antichymotrypsin, to cause a plasma deficiency that results in the clinical syndromes of thrombosis, angio-oedema and emphysema respectively. Understanding the common mechanism underlying the retention and deficiency of mutants of the serpins has allowed us to group these conditions as the serpinopathies. We review in this paper the molecular and structural basis of the serpinopathies and show how this has allowed the development of specific agents to block the polymerization that underlies disease.

We review here the molecular mechanisms that underlie alpha1-antitrypsin deficiency and show how an understanding of this mechanism has allowed us to explain the deficiency of other members of the serine proteinase inhibitor or serpin superfamily. These include the deficiency of antithrombin, C1-inhibitor and alpha1-antichymotrypsin in association with thrombosis, angio-oedema and emphysema respectively. Moreover the accumulation of mutant neuroserpin within neurones causes the novel dementia familial encephalopathy with neuroserpin inclusion bodies (FENIB). We have grouped these conditions together as the serpinopathies as recognition of their common pathophysiology provides a platform to develop strategies to treat the associated clinical syndromes.

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