Heteromeric Complexes of Native Collectin Kidney 1 and Collectin Liver 1 Are Found in the Circulation with MASPs and Activate the Complement System
Heteromeric Complexes of Native Collectin Kidney 1 and Collectin Liver 1 Are Found in the Circulation with MASPs and Activate the Complement System
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DOI：
10.4049/jimmunol.1302121
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发表时间：
2013-12-15
影响因子：
4.4
通讯作者：
Hansen, Soren
中科院分区：
文献类型：
--
作者：
Henriksen, Maiken L.;Brandt, Jette;Hansen, Soren
补体系统是先天免疫系统的重要组成部分。在甘露聚糖结合凝集素、纤维胶凝蛋白或肾聚集蛋白1（CL-K1，别名CL-11）与由碳水化合物或乙酰化分子组成的合适微生物模式结合后，补体级联反应可在凝集素活化途径下游启动。在从血浆中纯化和表征天然CL-K1的过程中，我们观察到肝聚集蛋白1（CL-L1）被共纯化。基于去糖基化和非还原/还原二维SDS-PAGE，我们在二硫桥稳定的复合物中检测到CL-K1和CL-L1。通过ELISA和瞬时共表达进一步显示了血浆中异聚体复合物的形成。从二维SDS-PAGE上的迁移模式判断，发现大部分血浆CL-K1与CL-L1复合。该复合物的比例有利于CL-K1，表明异聚亚基由一个CL-L1和两个CL-K1多肽链组成。我们发现，该复合物在体外以nM范围内的亲和力结合甘露聚糖结合凝集素相关丝氨酸蛋白酶（MASP），并且与血浆中的MASP-1/-3和MASP-2都相关。在MASP-2存在下结合甘露聚糖或DNA后，CL-L1-CL-K1复合物介导C4b的沉积。有利于大的寡聚体，复合物的活性部分由寡聚体的大小决定，这可能受到CL-K1的可变剪接变体的影响。天然异聚体复合物的活性上级于重组CL-K1的活性。我们的结论是，CL-K1存在于循环中的CL-L1与MASPs相互作用的异聚体复合物的形式，可以介导补体激活。
The complement system is an important part of the innate immune system. The complement cascade may be initiated downstream of the lectin activation pathway upon binding of mannan-binding lectin, ficolins, or collectin kidney 1 (CL-K1, alias CL-11) to suitable microbial patterns consisting of carbohydrates or acetylated molecules. During purification and characterization of native CL-K1 from plasma, we observed that collectin liver 1 (CL-L1) was copurified. Based on deglycosylation and nonreduced/ reduced two-dimensional SDS-PAGE, we detected CL-K1 and CL-L1 in disulfide bridge-stabilized complexes. Heteromeric complex formation in plasma was further shown by ELISA and transient coexpression. Judging from the migration pattern on two-dimensional SDS-PAGE, the majority of plasma CL-K1 was found in complex with CL-L1. The ratio of this complex was in favor of CL-K1, suggesting that a heteromeric subunit is composed of one CL-L1 and two CL-K1 polypeptide chains. We found that the complex bound to mannan-binding lectin-associated serine proteases (MASPs) with affinities in the nM range in vitro and was associated with both MASP-1/-3 and MASP-2 in plasma. Upon binding to mannan or DNA in the presence of MASP-2, the CL-L1-CL-K1 complex mediated deposition of C4b. In favor of large oligomers, the activity of the complex was partly determined by the oligomeric size, which may be influenced by an alternatively spliced variant of CL-K1. The activity of the native heteromeric complexes was superior to that of recombinant CL-K1. We conclude that CL-K1 exists in circulation in the form of heteromeric complexes with CL-L1 that interact with MASPs and can mediate complement activation.