Disruption of the Cys-5-Cys7 disulfide bridge in the platelet glycoprotein Ibβ prevents the normal maturation and surface exposure of GPIb-IX complexes
Disruption of the Cys-5-Cys7 disulfide bridge in the platelet glycoprotein Ibβ prevents the normal maturation and surface exposure of GPIb-IX complexes
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DOI：
10.1160/th03-01-0026
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发表时间：
2003-09-01
影响因子：
6.7
通讯作者：
Parrilla, R
中科院分区：
文献类型：
--
作者：
González-Manchón, C;Butta, N;Parrilla, R
本研究旨在阐明两个Bernard-Soulier综合征（BSS）表型相关患者的分子遗传缺陷。流式细胞术分析显示血小板糖蛋白（GP），Ibalpha和IX的检测水平，虽然血浆glycocalicin检测在这两种情况下。GP 1 α、GP 1 β和GP 1 X的完整测序揭示了GP 1 β密码子30中存在单个点突变，即G至A取代，其将Cys 5改变为Tyr。患者的父母和兄弟姐妹（该突变的杂合子）是无症状的，并且他们都显示GP 1 β α和GPIX的血小板含量降低。突变体GP 1 β亚基的瞬时转染不能使GP 1 β α表面表达，并且对GP 1 β-IX复合物的表面暴露产生显性负效应。转染细胞的代谢标记和免疫沉淀分析表明，[5 Tyr] GP 1b β可能与GPIX和GP 1ba相关，但GP 1b-IX复合物的成熟受损。用Ala取代Cys 5或Cys 7不能显示GP 1b-IX的表面表达，表明GP 1b β中的Cys 5-Cys 7二硫环对于GP 1b的有效加工和运输是必需的。GP 1b-IX复合物朝向质膜。我们的研究结果表明，所确定的新的GP 1b β突变是负责BSS表型的患者，并提供了一个解释的分子机制，减少血小板含量的GP 1b-IX复合物在杂合子个体。
This work aimed at elucidating the molecular genetic defect in two related patients with Bernard-Soulier syndrome (BSS) phenotype. Flow cytometric analysis revealed undetectable levels of platelet glycoproteins (GP), Ibalpha and IX, although plasma glycocalicin was detectable in both cases. The complete sequencing of GPlbalpha, GPlbbeta, and GPIX revealed the presence of a single point mutation, a G to A substitution, in codon 30 of GPlbbeta, that changes Cys5 to Tyr. The parents and sibling of the patients, heterozygotes for this mutation, were asymptomatic and they all showed a reduced platelet content of GPlbalpha and GPIX Transient transfection of the mutant GPlbbeta subunit failed to render surface expression of GPlbalpha and exerted a dominant-negative effect on the surface exposure of the GPlb-IX complex. Metabolic labelling and immunoprecipitation analysis of transfected cells indicated that [5Tyr]GPlbbeta may associate with GPIX and GPlba, but the maturation of the GPlb-IX complex is impaired. Substitution of either Cys5 or Cys7 by Ala failed to show surface expression of GPlb-IX, suggesting that the Cys5-Cys7 disulfide loop in GPlbbeta is essential for the efficient processing and trafficking of. GPlb-IX complexes toward the plasma membrane. Our findings indicate that the identified novel GPlbbeta mutation is responsible for the BSS phenotype of the patients and provide an explanation for the molecular mechanism underlying the reduced platelet content of GPlb-IX complex in the heterozygous individuals.