Molecular interaction between joining chain and immunoglobulin by BIA

免疫球蛋白（Ig）连接链(J)是猪的二聚体IgA和五聚体IgM聚合所必需的，并且在各种脊椎动物和无脊椎动物物种中具有很好的保守性。用鸡J链CDNA转化大肠杆菌，合成了分子量为25 kDa的鸡J链重组蛋白（rCJ）。采用BIA CORE 3000系统分析了rCJ与Igs的相互作用。结果表明，rCJ对α链和μ链的结合能力较强，而对人α链和μ链的结合能力较弱。抗人J链与rCJ的反应性明显弱于抗鸡J链。此外，用半胱氨酸残基取代丝氨酸的cDNA合成rCJ，分析其对鸡Igs的结合能力，结果表明α链和μ链之间没有抑制作用。从鸡基因组DNA文库中提取编码14kb的J链克隆。其基因结构有4个外显子，与人和小鼠具有高度的相似性。然而，在编码3.8 kb的5′区，与小鼠和奶牛相比，没有同源序列。用荧光素酶测定5'区缺失突变体的启动子活性，结果发现所有突变体都有荧光素酶活性。在上游3.8 ~ 3.3 kb处分离出0.5 kb的增强子区，并通过TRANSFUC数据库分析鉴定出NF-E2、USF-1、MyoD、CdxA和GATA3等转录结合位点。这些结果表明，鸡J链的转录机制可能与哺乳动物不同。

Immunoglobulin (Ig) Joining (J) chain is required for polymerization of pIgs such as dimeric IgA and pentameric IgM, and has a well-conserved feature among various vertebrate and invertebrate species. Recombinant protein of chicken J chain (rCJ), molecular mass of 25 kDa, was synthesized from E. coli transformed by chicken J chain CDNA. Interaction between rCJ and Igs was analyzed by BIA CORE 3000 system. In result, rCJ has a high binding capacity to α and μ chains but not those of human. The reactivity between anti-human J chain and rCJ was much weaker than that of anti-chicken J chain. In addition, rCJ was made from cDNA substituted by cysteine residue to serine and analyzed the binding capacity to chicken Igs, resulting that no inhibitory effect was detected between α and μ chains. Chicken genomic J chain clones encoding 14 kb were taken from DNA library. The structure of its gene has 4 exons having a high degree of similarities compared to that of human and mouse. However, in 5'-region encoding 3.8 kb, there is no homologous sequence compared to mouse and cow. Luciferase assay was performed to determine the promoter activity among deletion mutants derived from 5'-region, resulting that luciferase activities were observed in all mutans. Futhermore, enhancer region consisted of 0.5 kb was isolated from 3.8 kb to 3.3 kb upstream and several franscriptional binding sites, such as NF-E2, USF-1, MyoD, CdxA and GATA3, were identified using TRANSFUC data base analysis. These results suggest that transcriptional mechanism of the chicken J chain may be different from that of mammals.