Pillois Xavier, Peters Pierre, Segers Karin, Nurden Alan T
Institut de Rhythmologie et de Modélisation Cardiaque, Plateforme Technologique d'Innovation Biomédicale, Hôpital Xavier Arnozan, Bordeaux, France.
Université de Bordeaux, INSERM U1034, Bordeaux, France.
Mol Genet Genomic Med. 2018 Mar;6(2):249-260. doi: 10.1002/mgg3.365. Epub 2018 Jan 31.
Studies on the inherited bleeding disorder, Glanzmann thrombasthenia (GT), have helped define the role of the αIIbβ3 integrin in platelet aggregation. Stable bent αIIbβ3 undergoes conformation changes on activation allowing fibrinogen binding and its taking an extended form. The αIIb genu assures the fulcrum of the bent state. Our goal was to determine how structural changes induced by missense mutations in the αIIb genu define GT phenotype.
Sanger sequencing of ITGA2B and ITGB3 in the index case followed by in silico modeling of all known GT-causing missense mutations extending from the lower part of the β-propeller, and through the thigh and upper calf-1 domains.
A homozygous c.1772A>C transversion in exon 18 of ITGA2B coding for a p.Asp591Ala substitution in an interconnecting loop of the lower thigh domain of αIIb in a patient with platelets lacking αIIbβ3 led us to extend our in silico modeling to all 16 published disease-causing missense variants potentially affecting the αIIb genu. Modifications of structuring H-bonding were the major cause in the thigh domain although one mutation gave mRNA decay. In contrast, short-range changes induced in calf-1 appeared minor suggesting long-range effects. All result in severe to total loss of αIIbβ3 in platelets. The absence of mutations within a key Ca2+-binding loop in the genu led us to scan public databases; three potential single allele variants giving major structural changes were identiffied suggesting that this key region is not protected from genetic variation.
It appears that the αIIb genu is the object of stringent quality control to prevent platelets from circulating with activated and extended integrin.
对遗传性出血性疾病——Glanzmann血小板无力症（GT）的研究有助于明确αIIbβ3整合素在血小板聚集中的作用。稳定的弯曲αIIbβ3在激活时会发生构象变化，从而允许纤维蛋白原结合并呈现伸展形式。αIIb膝部确保了弯曲状态的支点。我们的目标是确定αIIb膝部错义突变引起的结构变化如何定义GT表型。
对索引病例的ITGA2B和ITGB3进行桑格测序，随后对所有已知的导致GT的错义突变进行计算机模拟，这些突变从β-螺旋桨的下部延伸至大腿和小腿-1上部结构域。
一名血小板缺乏αIIbβ3的患者中，ITGA2B第18外显子发生纯合的c.1772A>C颠换，编码αIIb大腿下部结构域连接环中的p.Asp591Ala替代，这使我们将计算机模拟扩展到所有16种已发表的可能影响αIIb膝部的致病错义变体。虽然有一个突变导致mRNA降解，但大腿结构域中氢键结构的改变是主要原因。相比之下，小腿-1中诱导的短程变化似乎较小，提示存在远程效应。所有这些都导致血小板中αIIbβ3严重至完全丧失。膝部关键Ca2+结合环内无突变，促使我们扫描公共数据库；鉴定出三个可能导致主要结构变化的潜在单等位基因变体，表明该关键区域无法免受遗传变异影响。
看来αIIb膝部是严格质量控制的对象，以防止血小板携带激活和伸展的整合素循环。
