Ronzoni Riccardo, Ferrarotti Ilaria, D'Acunto Emanuela, Balderacchi Alice M, Ottaviani Stefania, Lomas David A, Irving James A, Miranda Elena, Fra Annamaria
UCL Respiratory and the Institute of Structural and Molecular Biology, University College London, London WC1E 6JF, UK.
Pneumology Unit, Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, Department of Internal Medicine and Therapeutics, IRCCS San Matteo Hospital Foundation, University of Pavia, 27100 Pavia, Italy.
Int J Mol Sci. 2021 May 26;22(11):5668. doi: 10.3390/ijms22115668.
Alpha-1-antitrypsin (AAT) deficiency causes pulmonary disease due to decreased levels of circulating AAT and consequently unbalanced protease activity in the lungs. Deposition of specific AAT variants, such as the common Z AAT, within hepatocytes may also result in liver disease. These deposits are comprised of ordered polymers of AAT formed by an inter-molecular domain swap. The discovery and characterization of rare variants of AAT and other serpins have historically played a crucial role in the dissection of the structural mechanisms leading to AAT polymer formation. Here, we report a severely deficient shutter region variant, Bologna AAT (N186Y), which was identified in five unrelated subjects with different geographical origins. We characterized the new variant by expression in cellular models in comparison with known polymerogenic AAT variants. Bologna AAT showed secretion deficiency and intracellular accumulation as detergent-insoluble polymers. Extracellular polymers were detected in both the culture media of cells expressing Bologna AAT and in the plasma of a patient homozygous for this variant. Structural modelling revealed that the mutation disrupts the hydrogen bonding network in the AAT shutter region. These data support a crucial coordinating role for asparagine 186 and the importance of this network in promoting formation of the native structure.
α-1-抗胰蛋白酶（AAT）缺乏症会导致肺部疾病，原因是循环中的AAT水平降低，从而导致肺部蛋白酶活性失衡。特定AAT变体（如常见的Z型AAT）在肝细胞内沉积也可能导致肝脏疾病。这些沉积物由通过分子间结构域交换形成的AAT有序聚合物组成。AAT和其他丝氨酸蛋白酶抑制剂罕见变体的发现和表征在剖析导致AAT聚合物形成的结构机制方面一直发挥着关键作用。在此，我们报告了一种严重缺陷的快门区域变体，博洛尼亚AAT（N186Y），它在五名具有不同地理来源的无关受试者中被鉴定出来。我们通过在细胞模型中表达并与已知的致聚合物形成的AAT变体进行比较，对这种新变体进行了表征。博洛尼亚AAT表现出分泌缺陷和作为去污剂不溶性聚合物的细胞内积累。在表达博洛尼亚AAT的细胞培养基和该变体纯合子患者的血浆中均检测到细胞外聚合物。结构建模显示，该突变破坏了AAT快门区域的氢键网络。这些数据支持天冬酰胺186的关键协调作用以及该网络在促进天然结构形成中的重要性。
