A naturally occurring Tyr143His alpha IIb mutation abolishes alpha IIb beta 3 function for soluble ligands but retains its ability for mediating cell adhesion and clot retraction: comparison with other mutations causing ligand-binding defects.
A naturally occurring Tyr143His alpha IIb mutation abolishes alpha IIb beta 3 function for soluble ligands but retains its ability for mediating cell adhesion and clot retraction: comparison with other mutations causing ligand-binding defects.
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天然存在的 Tyr143His α IIb 突变消除了可溶性配体的 α IIb beta 3 功能，但保留了其介导细胞粘附和凝块收缩的能力：与导致配体结合缺陷的其他突变进行比较。
作者：
T. Kiyoi;Y. Tomiyama;S. Honda;S. Tadokoro;M. Arai;H. Kashiwagi;S. Kosugi;H. Kato;Y. Kurata;Y. Matsuzawa
原型非I结构域整合素α（IIb）β（3）与其配体之间相互作用的分子基础仍有待确定。在这项研究中，我们的特点是一个新的错义突变（Tyr 143 His）在α（IIb）与Glanzmann血小板无力症的变体。Osaka-12血小板表达大量的α（IIb）β（3）（对照的36%-41%），但不能结合可溶性配体，包括高亲和力的α（IIb）β（3）特异性肽模拟物拮抗剂。序列分析表明Osaka-12是一个复合杂合子，其单个（521）T>C取代导致α（IIb）中Tyr 143 His取代，并且不表达来自母体等位基因的α（IIb）mRNA。鉴于Tyr 143位于α（IIb）的β-螺旋桨结构域的W3 4-1环中，我们检测了Tyr 143 His或Tyr 143 Ala取代对α（IIb）β（3）表达和功能的影响，并与KO进行了比较。（在α（IIb）的160和161个残基之间插入Arg-Thr）和具有位于同一环中的Asp 163 Ala突变。它们中的每一种都消除了α（IIb）β（3）与可溶性配体的结合功能，而不干扰α（IIb）β（3）的表达。由于固定化纤维蛋白原和纤维蛋白是α（IIb）β（3）的高亲和力/亲合力配体，我们进行了细胞粘附和凝块收缩试验。与KO突变和Asp 163 Ala alpha（IIb）beta（3）形成鲜明对比，Tyr 143 His alpha（IIb）beta（3）表达细胞仍具有一定的细胞粘附和凝块收缩能力。因此，由Tyr 143 His α（IIb）诱导的功能缺陷可能是由其变构效应引起的，而不是由配体结合位点本身的缺陷引起的。这些详细的结构-功能分析提供了更好地了解整合素中的配体结合位点。
The molecular basis for the interaction between a prototypic non-I-domain integrin, alpha(IIb)beta(3), and its ligands remains to be determined. In this study, we have characterized a novel missense mutation (Tyr143His) in alpha(IIb) associated with a variant of Glanzmann thrombasthenia. Osaka-12 platelets expressed a substantial amount of alpha(IIb)beta(3) (36%-41% of control) but failed to bind soluble ligands, including a high-affinity alpha(IIb)beta(3)-specific peptidomimetic antagonist. Sequence analysis revealed that Osaka-12 is a compound heterozygote for a single (521)T>C substitution leading to a Tyr143His substitution in alpha(IIb) and for the null expression of alpha(IIb) mRNA from the maternal allele. Given that Tyr143 is located in the W3 4-1 loop of the beta-propeller domain of alpha(IIb), we examined the effects of Tyr143His or Tyr143Ala substitution on the expression and function of alpha(IIb)beta(3) and compared them with KO (Arg-Thr insertion between 160 and 161 residues of alpha(IIb)) and with the Asp163Ala mutation located in the same loop by using 293 cells. Each of them abolished the binding function of alpha(IIb)beta(3) for soluble ligands without disturbing alpha(IIb)beta(3) expression. Because immobilized fibrinogen and fibrin are higher affinity/avidity ligands for alpha(IIb)beta(3), we performed cell adhesion and clot retraction assays. In sharp contrast to KO mutation and Asp163Ala alpha(IIb)beta(3), Tyr143His alpha(IIb)beta(3)-expressing cells still had some ability for cell adhesion and clot retraction. Thus, the functional defect induced by Tyr143His alpha(IIb) is likely caused by its allosteric effect rather than by a defect in the ligand-binding site itself. These detailed structure-function analyses provide better understanding of the ligand-binding sites in integrins.