Conformational States of a Bacterial α2-Macroglobulin Resemble Those of Human Complement C3
Conformational States of a Bacterial α2-Macroglobulin Resemble Those of Human Complement C3
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DOI：
10.1371/journal.pone.0035384
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发表时间：
2012-04-17
期刊：
影响因子：
3.7
通讯作者：
Dessen, Andrea
中科院分区：
文献类型：
--
作者：
Neves, David;Estrozi, Leandro F.;Dessen, Andrea
α（2）巨球蛋白（α Ms-2）是广谱蛋白酶抑制剂，在真核生物的先天免疫系统中发挥重要作用。这些大的多结构域蛋白质的特征在于广谱诱饵区域和内部硫酯，其在切割时与靶蛋白酶共价缔合，从而允许其通过大的构象修饰被截留。值得注意的是，α Ms-2是更大的蛋白质超家族的一部分，该蛋白质超家族包括补体系统的蛋白质，例如C3，一种多结构域大分子，其特征还在于内部硫酯携带结构域，并且其活化代表补体级联中的关键步骤。最近，在大量细菌基因组中鉴定出α M-2/C3样基因，并且大肠杆菌α M-2同源物（ECAM）显示出被蛋白酶激活。在这项工作中，我们的结构特征ECAM的电子显微镜和小角散射（SAXS）技术。ECAM是一种细长的柔性分子，与非活性形式的C3具有总体相似性;通过甲胺、胰凝乳蛋白酶或弹性蛋白酶的活化诱导构象修饰，使人联想到C3转化为其活性形式C3 b所经历的构象修饰。此外，ECAM的C-末端显示出高度的灵活性和不同的构象，可能是伴侣大分子的识别位点。这项工作揭示了一种潜在的细菌防御机制，该机制模拟了真核生物中补体级联激活所必需的结构重排，并代表了开发抗菌药物的可能新靶点。
alpha(2) macroglobulins (alpha Ms-2) are broad-spectrum protease inhibitors that play essential roles in the innate immune system of eukaryotic species. These large, multi-domain proteins are characterized by a broad-spectrum bait region and an internal thioester, which, upon cleavage, becomes covalently associated to the target protease, allowing its entrapment by a large conformational modification. Notably, alpha Ms-2 are part of a larger protein superfamily that includes proteins of the complement system, such as C3, a multi-domain macromolecule which is also characterized by an internal thioester-carrying domain and whose activation represents the pivotal step in the complement cascade. Recently, alpha M-2/C3-like genes were identified in a large number of bacterial genomes, and the Escherichia coli alpha M-2 homolog (ECAM) was shown to be activated by proteases. In this work, we have structurally characterized ECAM by electron microscopy and small angle scattering (SAXS) techniques. ECAM is an elongated, flexible molecule with overall similarities to C3 in its inactive form; activation by methylamine, chymotrypsin, or elastase induces a conformational modification reminiscent of the one undergone by the transformation of C3 into its active form, C3b. In addition, the proposed C-terminus of ECAM displays high flexibility and different conformations, and could be the recognition site for partner macromolecules. This work sheds light on a potential bacterial defense mechanism that mimics structural rearrangements essential for activation of the complement cascade in eukaryotes, and represents a possible novel target for the development of antibacterials.