Molecular interaction between joining chain and immunoglobulin by BIA

免疫球蛋白(Ig)连接(J)链是猪二聚体IgA和五聚体IgM聚合所必需的，在各种脊椎动物和无脊椎动物中具有很好的保守性。以鸡J链CDNA转化大肠杆菌为原料，合成了相对分子质量为25 kDa的鸡J链重组蛋白。用BIA CORE 3000系统分析RCJ与IGS之间的相互作用。结果表明，RCJ对α和μ链有较高的结合能力，但对人的结合能力不强。抗人J链与RCJ的反应活性明显弱于抗鸡J链。此外，将半胱氨酸残基取代的c DNA与丝氨酸结合，分析其与鸡免疫球蛋白的结合能力，结果表明α和μ链之间没有抑制作用。从DNA文库中获得了编码14kb的鸡基因组J链克隆。它的基因结构有4个外显子，与人和小鼠的结构有很高的相似性。然而，在编码3.8kb的5‘端，没有与小鼠和牛的同源序列。用荧光素酶活性测定5‘端缺失突变株的启动子活性，结果表明所有突变株都有荧光素酶活性。进一步通过TRANSFUC数据库分析，从3.8kb到3.3kb的上游区域分离到0.5kb的增强子区域，并鉴定了几个转录结合位点，如NF-E2、USF-1、MyoD、CDxA和GATA3。这些结果表明，鸡J链的转录机制可能与哺乳动物的不同。

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.