Hydrophobic amino acid residues are critical for the immunodominant epitope of the goodpasture autoantigen - A molecular basis for the cryptic nature of the epitope
Hydrophobic amino acid residues are critical for the immunodominant epitope of the goodpasture autoantigen - A molecular basis for the cryptic nature of the epitope
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DOI：
10.1074/jbc.m008956200
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发表时间：
2001-03-02
影响因子：
4.8
通讯作者：
Hudson, BC
中科院分区：
文献类型：
--
作者：
David, M;Borza, DB;Hudson, BC
Goodpasture（GP）自身免疫性疾病是由IV型胶原蛋白的自身抗体结合到肾小球基底膜引起的，导致快速进展的肾小球肾炎。免疫显性GP（A）自身表位被α 3（IV）链的非胶原（NC 1）结构域内的残基17-31（E-A区）所涵盖。GP表位隐藏在NC 1六聚体复合物中，该复合物存在于组织中发现的IV型胶原网络中，并且除非六聚体解离，否则自身抗体无法接近。相比之下，Mab 3单克隆抗体的表位也位于E-A区内，但在六聚体复合物中是完全可接近的。在这项研究中，确定了组成GP（A）自身表位的残基的身份，并探索了其隐藏性质的分子基础。这是使用定点诱变将E-A区中的α 3（IV）残基与同源但非免疫反应性的α 1（IV）NC 1结构域的相应残基交换，然后比较突变嵌合体与GP（A）和Mab 3抗体的反应性来实现的。结果表明，三个疏水残基（Ala（18）、Ile（19）和瓦尔（27））和Pro（28）对于GP（A）自身表位是关键的，而两个亲水残基（Ser（21）和Ser（31））沿着Pro（28）对于Mab 3表位是关键的。这些结果表明GP（A）自身表位的隐蔽性质是六聚体复合物的α 3、α 4和α 5 NC 1结构域的四级相互作用的结果，所述四级相互作用掩埋了一个或多个疏水残基。这些发现为理解该疾病的病因和发病机制以及设计将模拟表位并因此阻断GP自身抗体与自身抗原结合的药物提供了关键信息。
Goodpasture (GP) autoimmune disease is caused by autoantibodies to type IV collagen that bind to the glomerular basement membrane, causing rapidly progressing glomerulonephritis. The immunodominant GP(A) autoepitope is encompassed by residues 17-31 (the E-A region) within the noncollagenous (NC1) domain of the alpha3(IV) chain. The GP epitope is cryptic in the NC1 hexamer complex that occurs in the type IV collagen network found in tissues and inaccessible to autoantibodies unless the hexamer dissociates. In contrast, the epitope for the Mab3 monoclonal antibody is also located within the E-A region, but is fully accessible in the hexamer complex. In this study, the identity of residues that compose the GP(A) autoepitope was determined, and the molecular basis of its cryptic nature was explored. This was achieved using site-directed mutagenesis to exchange the alpha3(IV) residues in the E-A region with the corresponding residues of the homologous but non-immunoreactive alpha1(IV) NC1 domain and then comparing the reactivity of the mutated chimeras with GP(A) and Mab3 antibodies. It was shown that three hydrophobic residues (Ala(18), Ile(19), and Val(27)) and Pro(28) are critical for the GP(A) autoepitope, whereas two hydrophilic residues (Ser(21) and Ser(31)) along with pro(28) are critical for the Mab3 epitope. These results suggest that the cryptic nature of the GP(A) autoepitope is the result of quaternary interactions of the alpha3, alpha4, and alpha5 NC1 domains of the hexamer complex that bury the one or more hydrophobic residues. These findings provide critical information for understanding the etiology and pathogenesis of the disease as well as for designing drugs that would mimic the epitope and thus block the binding of GP autoantibodies to autoantigen.