The binding affinity of human IgG for its high affinity Fc receptor is determined by multiple amino acids in the CH2 domain and is modulated by the hinge region.
The binding affinity of human IgG for its high affinity Fc receptor is determined by multiple amino acids in the CH2 domain and is modulated by the hinge region.
复制标题
DOI：
10.1084/jem.173.6.1483
复制
发表时间：
1991-06-01
期刊：
影响因子：
--
通讯作者：
Morrison SL
中科院分区：
文献类型：
--
作者：
Canfield SM;Morrison SL
一个嵌合免疫球蛋白家族（Igs）具有针对与人IgG1， -2， -3和-4连接的半抗原丹酰的小鼠可变区，已被鉴定为与人高亲和力Fc γ受体Fc γ RI结合。嵌合IgG1和-3具有最高的亲和关联（Ka = 10(9) M-1）， IgG4在此基础上降低了10倍，IgG2未显示可检测到的结合。在一系列基因操作中，来自强结合亚类IgG3的结构域与来自非结合亚类IgG2的结构域进行了交换。发现CH2结构域的亚类是决定IgG受体亲和力的关键。此外，研究发现铰链区调节了IgG对Fc γ RI的亲和力，可能是通过决定Fc γ RI对Fc结合位点的可及性来实现的。根据结合和非结合IgG亚类的同源性比较，在IgG3和IgG4的CH2结构域上进行了一系列氨基酸替换，这些位点被认为对Fc受体结合可能重要。这些突变体的特征揭示了在初级结构中相隔近100个残基的遗传CH2结构域的两个区域的Fc γ RI关联的重要性。其中第一个是铰链连接或较低的铰链区域，其中两个残基，IgG1和-3中的Leu（234）和Leu(235)，对高亲和力结合至关重要。在这两个位点中的任何一个位置上进行替换都会使IgG的结合常数降低10-100倍。第二个似乎有助于受体结合的区域位于CH2结构域内两条β链之间的铰链-近端弯曲处，特别是IgG1和-3中的Pro（331）。由于在该结构域中形成β片，该残基位于铰链连接区域的11a内。该位点的取代使Fc受体结合常数降低了10倍。
A family of chimeric immunoglobulins (Igs) bearing the murine variable region directed against the hapten dansyl linked to human IgG1, -2, -3, and -4 has been characterized with respect to binding to the human high affinity Fc gamma receptor, Fc gamma RI. Chimeric IgG1 and -3 have the highest affinity association (Ka = 10(9) M-1), IgG4 is 10-fold reduced from this level, and IgG2 displays no detectable binding. A series of genetic manipulations was undertaken in which domains from the strongly binding subclass IgG3 were exchanged with domains from the nonbinding subclass IgG2. The subclass of the CH2 domain was found to be critical for determining IgG receptor affinity. In addition, the hinge region was found to modulate the affinity of the IgG for Fc gamma RI, possibly by determining accessibility of Fc gamma RI to the binding site on Fc. A series of amino acid substitutions were engineered into the CH2 domain of IgG3 and IgG4 at sites considered potentially important to Fc receptor binding based on homology comparisons of binding and nonbinding IgG subclasses. Characterization of these mutants has revealed the importance for Fc gamma RI association of two regions of the genetic CH2 domain separated in primary structure by nearly 100 residues. The first of these is the hinge-link or lower hinge regions, in which two residues, Leu (234) and Leu(235) in IgG1 and -3, are critical to high affinity binding. Substitution at either of these sites reduces the IgG association constant by 10-100-fold. The second region that appears to contribute to receptor binding is in a hinge- proximal bend between two beta strands within the CH2 domain, specifically, Pro(331) in IgG1 and -3. As a result of beta sheet formation within this domain, this residue lies within 11 A of the hinge-link region. Substitution at this site reduces the Fc receptor association constant by 10-fold.