Activation of the classical complement pathway by mannose-binding protein in association with a novel C1s-like serine protease.
Activation of the classical complement pathway by mannose-binding protein in association with a novel C1s-like serine protease.
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甘露糖结合蛋白与新型C1样丝氨酸蛋白酶相关的经典补体途径的激活。
DOI：
10.1084/jem.176.6.1497
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发表时间：
1992-12-01
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血清甘露糖结合蛋白（MBP）是一种C型凝集素，可与某些病原体表面的甘露糖和N-乙酰葡糖胺末端结合，激活经典的补体途径。在本研究中，我们描述了MBP激活的机制。在钙离子存在下，通过在甘露聚糖-琼脂糖、抗-IgM-琼脂糖和抗-MBP-琼脂糖上的连续亲和层析获得人血清MBP组分。该馏分含有C1 s样丝氨酸蛋白酶，通过C4消耗进行评估。在乙二胺四乙酸存在下，通过反MBP-Sepharose再层析从MBP中分离C1 s样丝氨酸蛋白酶，命名为MBP相关丝氨酸蛋白酶（MASP）。MASP表现出C4和C2消费活动。MASP的分子量估计为83 kD，具有通过二硫键连接的重链（66 kD）和轻链（L）（31 kD）的两个多肽。负责蛋白酶活性的丝氨酸残基位于L链上。使用MASP和MBP的重构实验揭示了两种组分的组合恢复了对甘露聚糖的C4-和C2-活化能力。基于分子大小、抗原性和L链11个NH 2-末端氨基酸序列的分析，我们得出结论MASP是一种不同于C1 r或C1 s的新蛋白。我们的发现与MBP利用C1 r2-C1 s2复合物启动经典补体途径的机制不雅阁。
Serum mannose-binding protein (MBP) is a C-type lectin that binds to terminal mannose and N-acetylglucosamine moieties present on surfaces of certain pathogens and activates the classical complement pathway. In the present study, we describe the mechanism underlying the activation triggered by MBP. The human serum MBP fraction was obtained by sequential affinity chromatography on mannan-Sepharose, anti-IgM- Sepharose and anti-MBP-Sepharose in the presence of calcium ions. This fraction contained a C1s-like serine protease as assessed by C4 consumption. The C1s-like serine protease, designated MBP-associated serine protease (MASP), was separated from MBP by rechromatography on anti-MBP-Sepharose in the presence of ethylenediaminetetraacetic acid. MASP exhibited both C4- and C2-consuming activities. The molecular mass of MASP was estimated to be 83 kD with two polypeptides of heavy (66 kD) and light (L) (31 kD) chains linked by disulfide bonds. The serine residue responsible for protease activity is located on the L chain. Reconstitution experiments using MASP and MBP revealed that combination of the two components restores C4- and C2-activating capacity on mannan. Based on analyses of molecular size, antigenicity, and 11 NH2- terminal amino acid sequences of the L chain, we conclude that MASP is a novel protein different from C1r or C1s. Our findings are not in accord with a proposed mechanism by which MBP utilizes the C1r2-C1s2 complex to initiate the classical complement pathway.