The structure of MBL-associated serine protease-2 reveals that identical substrate Specificities of C1s and MASP-2 are realized through different sets of enzyme-substrate interactions
The structure of MBL-associated serine protease-2 reveals that identical substrate Specificities of C1s and MASP-2 are realized through different sets of enzyme-substrate interactions
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DOI：
10.1016/j.jmb.2004.07.014
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发表时间：
2004-10-01
影响因子：
5.6
通讯作者：
Závodszky, P
中科院分区：
文献类型：
--
作者：
Harmat, V;Gál, P;Závodszky, P
一个丝氨酸蛋白酶家族介导脊椎动物中几种防御机制的蛋白水解级联反应，如补体系统、血液凝固和纤维蛋白溶解。这些蛋白酶通常与其他糖蛋白形成大的复合物。它们的共同特征是它们的模块化结构和受限的底物特异性。补体的凝集素途径（其中甘露糖结合凝集素（MBL）识别病原体上的碳水化合物结构）被甘露糖结合凝集素相关丝氨酸蛋白酶-2（MASP-2）激活。我们呈现了MASP-2的催化片段的2.25埃分辨率结构，其包含第二补体控制蛋白模块（CCP 2）和丝氨酸蛋白酶（SP）结构域。如差示扫描量热法测量所示，CCP 2模块稳定SP结构域的结构。不对称单元包含两个具有不同CCP-SP结构域取向的分子，反映了CCP 2/SP接合处的模块化灵活性增加。这种灵活性可以部分解释MASP-2二聚体单独执行其所有功能的能力，而相同的功能由经典途径的C1复合物中大得多的C1 r（2）-C1 s（2）四聚体介导。MASP-2 SP结构域的主要支架是胰凝乳蛋白酶样的。8个表面环决定了S1和其他亚位点特异性。令人惊讶的是，形成S1口袋的MASP-2的一些表面环（例如环1和环2）与胰蛋白酶的那些类似，并且如果与Cl的那些相比则显示出显著差异，表明Cl和MASP-2的几乎相同的底物特异性通过不同组的酶-底物相互作用实现。(C)2004爱思唯尔有限公司保留所有权利。
A family of serine proteases mediates the proteolytic cascades of several defense mechanisms in vertebrates, such as the complement system, blood coagulation and fibrinolysis. These proteases usually form large complexes with other glycoproteins. Their common features are their modular structures and restricted substrate specificities. The lectin pathway of complement, where mannose-binding lectin (MBL) recognizes the carbohydrate structures on pathogens, is activated by mannose-binding lectin associated serine protease-2 (MASP-2). We present the 2.25 Angstrom resolution structure of the catalytic fragment of MASP-2 encompassing the second complement control protein module (CCP2) and the serine protease (SP) domain. The CCP2 module stabilizes the structure of the SP domain as demonstrated by differential scanning calorimetry measurements. The asymmetric unit contains two molecules with different CCP-SP domain orientations, reflecting increased modular flexibility at the CCP2/SP joint. This flexibility may partly explain the ability of the MASP-2 dimer to perform all of its functions alone, whereas the same functions are mediated by the much larger C1r(2)-C1s(2) tetramer in the C1 complex of the classical pathway. The main scaffold of the MASP-2 SP domain is chymotrypsin-like. Eight surface loops determine the S1 and other subsite specificities. Surprisingly, some surface loops of MASP-2, e.g. loop 1 and loop 2, which form the SI pocket are similar to those of trypsin, and show significant differences if compared with those of C1s, indicating that the nearly identical substrate specificities of C1s and MASP-2 are realized through different sets of enzyme-substrate interactions. (C) 2004 Elsevier Ltd. All rights reserved.