ANALYSIS OF THE PH-DEPENDENCE OF THE NEONATAL FC RECEPTOR IMMUNOGLOBULIN-G INTERACTION USING ANTIBODY AND RECEPTOR VARIANT
ANALYSIS OF THE PH-DEPENDENCE OF THE NEONATAL FC RECEPTOR IMMUNOGLOBULIN-G INTERACTION USING ANTIBODY AND RECEPTOR VARIANT
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DOI：
10.1021/bi00045a005
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发表时间：
1995-11-14
期刊：
影响因子：
2.9
通讯作者：
BJORKMAN, PJ
中科院分区：
文献类型：
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作者：
RAGHAVAN, M;BONAGURA, VR;BJORKMAN, PJ
新生儿Fc受体（FcRn）在肠道（pH 6.0-6.5）中结合来自摄入乳汁的母体免疫球蛋白G（IgG），并将其递送至新生儿血流（pH 7.0-7.5）。可溶形式的FcRn再现与IgG的生理pH依赖性相互作用，在pH 6.0-6.5下显示高亲和力结合，但在pH 7.0-7.5下显示弱结合或不结合。我们已经研究了pH依赖的FcRn/IgG相互作用，使用表面等离子体共振测定来测量动力学和平衡常数。我们发现，当pH从6.0升高到7.0时，FcRn对IgG的亲和力降低约2个数量级。希尔图分析表明，几个滴定残基参与pH依赖性的亲和力转变。组氨酸侧链可能是在pH 6.0和7.0之间滴定的残基的候选物，并且先前的生物化学和结构工作在IgG的Fc部分上鉴定了位于FcRn结合位点的几个组氨酸。使用在IgG/FcRn界面的组氨酸数目不同的突变Ige分子和IgG亚型变体，我们证明了位于C（H）2和C（H）3结构域之间的连接处的IgG组氨酸（残基310和433）有助于pH依赖性亲和力转变。使用突变FcRn分子的实验表明，FcRn重链上的两个组氨酸（残基250和251）也有助于FcRn/IgG相互作用的pH依赖性。使用FcRn和FcRn/Fc复合物的晶体结构解释这些结果。
The neonatal Fc receptor (FcRn) binds maternal immunoglobulin G (IgG) from ingested milk in the gut (pH 6.0-6.5) and delivers it to the bloodstream of the newborn (pH 7.0-7.5). A soluble version of FcRn reproduces the physiological pH-dependent interaction with IgG, showing high-affinity binding at pH 6.0-6.5 but weak or no binding at pH 7.0-7.5. We have studied the pH dependence of the FcRn/IgG interaction using a surface plasmon resonance assay to measure kinetic and equilibrium constants. We show that the affinity of FcRn for IgG is reduced about 2 orders of magnitude as the pH is raised from 6.0 to 7.0. A Hill plot analysis suggests that several titrating residues participate in the pH-dependent affinity transition. Histidine side chains are likely candidates for residues that titrate between pH 6.0 and 7.0, and previous biochemical and structural work identified several histidines on the Fc portion of IgG that are located at the FcRn binding site. Using mutant Ige molecules and IgG subtype variants that differ in the number of histidines at the IgG/FcRn interface, we demonstrate that IgG histidines located at the junction between the C(H)2 and C(H)3 domains (residues 310 and 433) contribute to the pH-dependent affinity transition. Experiments with a mutant FcRn molecule show that two histidines on the FcRn heavy chain (residues 250 and 251) also contribute to the pH dependence of the FcRn/IgG interaction. These results are interpreted using the crystal structures of FcRn and an FcRn/Fc complex.