Interaction of Human C1q with IgG and IgM: Revisited
Interaction of Human C1q with IgG and IgM: Revisited
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DOI：
10.1021/bi801131h
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发表时间：
2008-12-09
期刊：
影响因子：
2.9
通讯作者：
Kojouharova, Mihaela S.
中科院分区：
文献类型：
--
作者：
Gadjeva, Mihaela G.;Rouseva, Marieta M.;Kojouharova, Mihaela S.
激活经典补体途径的第一步涉及球状 C1q 结构蛋白 (gC1q) 与抗原结合的 IgG 或 IgM 的结合。为了加深对 gC1q 与 IgG 和 IgM 相互作用机制的理解，我们比较了 A 链和 C 链各个球状模块的单残基突变体的免疫球蛋白结合特性。我们发现 LyS(A200) 和 Lys(C170) 对于与两种免疫球蛋白的结合都很重要。此外，在表位作图分析中使用了两种被称为C1q-IgG和-IgM相互作用的有效抑制剂的C1q特异性scFv抗体。鉴定了参与scFv的Clq表位的一组重要残基：用于scFv3(V)表位的LysC170以及用于scFv10(V)表位的Arg(B108)和Arg(B109)。 scFv3(V)和scFv10(V)结合预先形成的Clq-IgG或Clq-IgM复合物的能力不同：scFv3(V)保留其结合Clq的能力，而scFv10(V)失去其结合能力。考虑到表位的不同位置以及两种抗体结合Clq-IgG和Clq-IgM复合物的不同能力，我们发现Clq顶端表面的残基[scFv3(V)表位所在的位置]参与了IgG和IgM的初始识别，而Arg(B108)和Arg(B109)能够在初始识别期间以及免疫球蛋白的最终结合期间相互作用。报道的结果提供了第一个实验证据，支持以下观点：在与特定 Clq 配体相互作用期间，gClq 重新定向后，gClq 的顶面和赤道表面连续参与。
The first step of activation of the classical complement pathway involves the binding of the globular C1q dornain (gC1q) to the antigen-bound IgG or IgM. To improve our understanding of the mechanism of interaction of gC1q with IgG and IgM, we compared the immunoglobulin binding properties of single-residue mutants of individual globular modules of A and C chains. We found that LyS(A200) and Lys(C170) are significant for binding with both immunoglobulins. In addition, two Clq-specific scFv antibodies known as potent inhibitors of C I q-IgG and -IgM interactions were used in the epitope mapping analysis. A set of important residues, which participate in the Clq epitopes for scFv, were identified: LysC170 for the scFv3(V) epitope and Arg(B108) and Arg(B109) for the scFv10(V) epitope. The ability of scFv3(V) and scFv10(V) to bind preformed Clq-IgG or Clq-IgM complexes differed: scFv3(V) retained its ability to bind Clq, while scFv10(V) lost it. Given the different locations of the epitopes and the varying abilities of both antibodies to bind Clq-IgG and Clq-IgM complexes, we found that residues from the apical surface of Clq [where the scFv3(V) epitope was located] were involved in the initial recognition of IgG and IgM, while Arg(B108) and Arg(B109) are able to interact during the initial recognition as well as during the final binding of immunoglobulins. The reported results provide the first experimental evidence supporting the notion that apical and equatorial surfaces of gClq have consecutive involvement following the gClq reorientation during the interaction with specific Clq ligands.