EXPRESSION AND CRYSTALLIZATION OF A SOLUBLE AND FUNCTIONAL FORM OF AN FC RECEPTOR RELATED TO CLASS-I HISTOCOMPATIBILITY MOLECULES
EXPRESSION AND CRYSTALLIZATION OF A SOLUBLE AND FUNCTIONAL FORM OF AN FC RECEPTOR RELATED TO CLASS-I HISTOCOMPATIBILITY MOLECULES
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DOI：
10.1073/pnas.89.2.638
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发表时间：
1992-01-15
影响因子：
11.1
通讯作者：
BJORKMAN, PJ
中科院分区：
文献类型：
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作者：
GASTINEL, LN;SIMISTER, NE;BJORKMAN, PJ
母亲将免疫球蛋白转运到新生哺乳动物对于独立生命的第一周期间的免疫防御是重要的。IgG的Fc部分的受体介导免疫球蛋白通过肠上皮细胞从乳汁转移到新生小鼠和大鼠的血流中。新生儿Fc受体（FcRn）从乳鼠肠上皮细胞中分离出来，与I类组织相容性分子有着惊人的相似之处。FcRn的重链在三个胞外结构域中与I类分子的相应结构域具有序列相似性，两种类型分子的轻链均为β-2-微球蛋白。为了促进FcRn的生化表征和结晶，我们表达了一种分泌形式以及两种不同的可通过磷脂酶处理溶解的脂质连接形式。脂质连接形式是由β-2-微球蛋白和重链的细胞外部分组成的异二聚体，并通过与重链或β-2-微球蛋白连接的磷脂酰肌醇键锚定在膜上。表达任一脂质连接形式的细胞结合大鼠Fc，再现已知的结合的生理pH依赖性。分泌的FcRn已经以高达40 mg/L的产率从细胞上清液中纯化。可溶性FcRn的圆二色性光谱似乎与I类MHC分子的光谱相似，这表明一级序列的相似性也延伸到二级结构的相似性。可溶性FcRn以适合通过X射线衍射方法进行结构测定的形式结晶，这将最终允许对两种类型的分子进行详细比较。
Maternal transport of immunoglobulin to the newborn mammal is important for immune defense during the first weeks of independent life. Receptors for the Fc portion of IgG mediate the transfer of immunoglobulin from milk to the bloodstream of newborn mice and rats, by passage through intestinal epithelial cells. Neonatal Fc receptors (FcRn) isolated from intestinal epithelial cells of suckling rats bear a striking resemblance to class I histocompatibility molecules. The heavy chain of FcRn has sequence similarity in three extracellular domains to the corresponding domains of class I molecules, and the light chain of both types of molecules is beta-2-microglobulin. To facilitate biochemical characterization and crystallization of FcRn, we have expressed a secreted form, as well as two different lipid-linked forms solubilizable by phospholipase treatment. The lipid-linked forms are heterodimers consisting of beta-2-microglobulin and the extracellular portion of the heavy chain and are anchored to the membrane by a phosphatidylinositol linkage attached to either the heavy chain or beta-2-microglobulin. Cells expressing either lipid-linked form bind rat Fc, reproducing the known physiological pH dependence of binding. Secreted FcRn has been purified in yields up to 40 mg/liter from cell supernatants. Circular dichroism spectra of soluble FcRn appear similar to spectra of class I MHC molecules, suggesting that the similarities in primary sequence extend also to a similarity in secondary structure. Soluble FcRn crystallizes in a form amenable to a structure determination by x-ray diffraction methods, which will ultimately allow a detailed comparison of the two types of molecules.