Localization of the binding site for the monocyte immunoglobulin (Ig) A-Fc receptor (CD89) to the domain boundary between C alpha 2 and C alpha 3 in human IgA1
Localization of the binding site for the monocyte immunoglobulin (Ig) A-Fc receptor (CD89) to the domain boundary between C alpha 2 and C alpha 3 in human IgA1
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DOI：
10.1084/jem.183.4.1579
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发表时间：
1996-04-01
影响因子：
15.3
通讯作者：
Capra, JD
中科院分区：
文献类型：
--
作者：
Carayannopoulos, L;Hexham, JM;Capra, JD
免疫球蛋白（IG）A作为所有粘膜表面的第一道体液防御，大量存在于血液中。在体液免疫中发挥其作用时，伊加与血清中以及免疫细胞和炎性细胞表面上存在的多种效应分子相互作用。为了研究这些相互作用，我们以前建立了人类IgA 1在昆虫细胞中使用重组杆状病毒的表达，并表明，表达的抗体是一个结构和功能完整的多肽，用于检查伊加的分子特性。事实上，由于C α 2 N-连接的糖基化位点位于C α 2的Fab远端极附近，缺乏C α 2 N-糖基化的突变体IgA 1不能结合其同源受体，这表明单核细胞Fc α受体（mFc α R）在包含C α 2和C α 3结构域之间的边界的铰链远端位点识别伊加。在这份报告中，我们利用结构域交换的伊加/IgG和点突变的伊加嵌合体来验证上述假设。使用抗原特异性重置测定和mFc α R表达细胞系，我们表明：（a）C α 2和C α 3一起对于结合是必需的和充分的;（B）伊萨铰链和尾片段对于结合都不是必需的;（c）远离结构域间边界的突变不影响结合;和（d）位于C α 2和C α 3之间的三维边界附近的突变完全破坏结合。综上所述，这些结果将伊加上的mFc α R识别位点定位于第二和第三恒定结构域之间的边界区域-该位点类似于IgG上的金黄色葡萄球菌蛋白A识别的位点。迄今为止，这种铰链远端位点的使用在IG超家族的Fc受体中是独特的。
Immunoglobulin (Ig) A serves as the first line of humoral defense at all mucosal surfaces and is present in large quantities in blood. In playing its role in humoral immunity, IgA interacts with a variety of effector molecules present both in serum and on the surfaces of immune and inflammatory cells. To study these interactions, we previously established expression of human IgA1 in insect cells using recombinant baculoviruses and showed that the expressed antibody is a structurally and functionally intact polypeptide useful for examining the molecular properties of IgA. Indeed, since the C alpha 2 N-linked glycosylation site lies near the Fab-distal pole of C alpha 2, the inability of a mutant IgA1 lacking C alpha 2 N-glycosylation to bind its cognate receptor suggested that the monocyte Fc alpha receptor (mFc alpha R) recognizes IgA at a hinge-distal site encompassing the boundary between the C alpha 2 and C alpha 3 domains. In this report, we utilize both domain-swapped IgA/IgG and point-mutated IgA chimeras to verify the above hypothesis. Using an antigen-specific resetting assay and a mFc alpha R-expressing cell line, we show that: (a) C alpha 2 and C alpha 3 together are necessary and sufficient for binding; (b) neither the ISA hinge nor the tailpiece is necessary for binding; (c) mutations away from the interdomain boundary do not affect binding; and (d) mutations located near the three-dimensional boundary between C alpha 2 and C alpha 3 completely disrupt binding. Taken together, these results localize the mFc alpha R recognition site on IgA to the boundary region between the second and third constant domains - a site analogous to that recognized by Staphylococcus aureus protein A on IgG. The use of this hinge-distal site is, to date, unique among Fc receptors of the Ig superfamily.