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    Deficiency mutations of Alpha-1 Antitrypsin. Effects on folding, function, and polymerization

    Haq, Imran and Irving, James and Saleh, A.D. and Dron, L. and Regan-Mochrie, G.L. and Motamedi-Shad, Neda and Hurst, J.R. and Gooptu, Bibekbrata and Lomas, David (2016) Deficiency mutations of Alpha-1 Antitrypsin. Effects on folding, function, and polymerization. American Journal of Respiratory Cell and Molecular Biology 54 (1), pp. 71-80. ISSN 1044-1549.

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    Abstract

    Misfolding, polymerization, and defective secretion of functional alpha-1 antitrypsin underlies the predisposition to severe liver and lung disease in alpha-1 antitrypsin deficiency. We have identified a novel (Ala336Pro, Baghdad) deficiency variant and characterized it relative to the wild-type (M) and Glu342Lys (Z) alleles. The index case is a homozygous individual of consanguineous parentage, with levels of circulating alpha-1 antitrypsin in the moderate deficiency range, but is a biochemical phenotype that could not be classified by standard methods. The majority of the protein was present as functionally inactive polymer, and the remaining monomer was 37% active relative to the wild-type protein. These factors combined indicate an 85 to 95% functional deficiency, similar to that seen with ZZ homozygotes. Biochemical, biophysical, and computational studies further defined the molecular basis of this deficiency. These studies demonstrated that native Ala336Pro alpha-1 antitrypsin could populate the polymerogenic intermediate—and therefore polymerize—more readily than either wild-type alpha-1 antitrypsin or the Z variant. In contrast, folding was far less impaired in Ala336Pro alpha-1 antitrypsin than in the Z variant. The data are consistent with a disparate contribution by the “breach” region and “shutter” region of strand 5A to folding and polymerization mechanisms. Moreover, the findings demonstrate that, in these variants, folding efficiency does not correlate directly with the tendency to polymerize in vitro or in vivo. They therefore differentiate generalized misfolding from polymerization tendencies in missense variants of alpha-1 antitrypsin. Clinically, they further support the need to quantify loss-of-function in alpha-1 antitrypsin deficiency to individualize patient care.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): alpha-1 antitrypsin deficiency, polymerization, mutation, unfolding, serpinopathies
    School: Birkbeck Schools and Departments > School of Science > Biological Sciences
    Depositing User: Administrator
    Date Deposited: 17 May 2016 16:27
    Last Modified: 17 May 2016 16:27
    URI: http://eprints.bbk.ac.uk/id/eprint/15214

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