Binding of the pentamer/hexamer forms of mannan-binding protein to zymosan activates the proenzyme C1r2C1s2 complex, of the classical pathway of complement, without involvement of C1q.
Binding of the pentamer/hexamer forms of mannan-binding protein to zymosan activates the proenzyme C1r2C1s2 complex, of the classical pathway of complement, without involvement of C1q.
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甘露聚糖结合蛋白的五聚体/六聚体形式与酵母聚糖的结合可激活补体经典途径的酶原 C1r2C1s2 复合物，而无需 C1q 的参与。
作者：
Jinhua Lu;S. Thiel;H. Wiedemann;R. Timpl;K. Reid
用甘露聚糖-琼脂糖亲和层析、凝胶过滤和离子交换层析、抗IgM琼脂糖柱层析，从混合的正常人血清中分离得到甘露聚糖结合蛋白(MBP)，产率为40微克/升。用纯化的MBP制备兔抗血清，利用多克隆抗体的特异性和MBP依赖于钙离子的碳水化合物结合特性，建立了一种酶联免疫分析方法。对103名献血者的血清检测显示，MBP水平从0微克/升到870微克/升不等。MBP与酵母多糖相互作用后，可有效地激活C1r2125I-C1s2复合体，该复合体是通过125I-C1s2与来自C1q完全遗传缺陷患者的血清孵育而制备的，然后经Sepharose6B凝胶过滤。纯化的MBP由三聚体、四聚体、五聚体和六聚体的混合物组成，层析、SDS-PAGE和电子显微镜研究表明，MBP的结构单位约为90 kDa。只有五聚体/六聚体部分中的分子与C1q具有相似的整体结构，似乎能引起C1r2C1s2复合体中C1s的有效激活，依赖于酵母多糖。因此，在某些感染的早期阶段，MBP的五聚体/六聚体形式可能在C系统的抗体非依赖性激活中发挥重要作用。
The serum lectin, mannan binding protein (MBP), was isolated in a yield of 40 micrograms/liter from pooled normal human serum by affinity chromatography on mannan-Sepharose, followed by gel-filtration and ion-exchange chromatography and finally by passage down an anti-IgM Sepharose column. A rabbit antiserum was prepared against the purified MBP and an enzyme-linked immunoassay developed that used both the specificity of the polyclonal antibody and the Ca+(+)-dependent carbohydrate binding property of MBP. Assay of the sera from 103 blood-donors showed a wide range of MBP levels, ranging from 0 to 870 micrograms/liter. MBP, after interaction with zymosan, caused efficient activation of a C1r2 125I-C1s2 complex that was prepared by incubation of 125I-C1s2 with serum, from a patient with a complete genetic deficiency of C1q, followed by gel-filtration on Sepharose 6B. The purified MBP is composed of a mixture of trimers, tetramers, pentamers, and hexamers of an approximate 90-kDa structural unit as judged by chromatography, SDS-PAGE and electron microscopy studies. Only the molecules in the pentamer/hexamer fraction, which have a similar overall structure to that of C1q, appeared to cause efficient, zymosan-dependent, activation of C1s within the C1r2C1s2 complex. The pentamer/hexamer form of MBP may therefore play an important role in antibody-independent activation of the C system during the early stages of certain infections.