Boisset N, Taveau J C, Barray M, Van Leuven F, Delain E, Lamy J N
Laboratoire de Biochimie Fondamentale et URA225 CNRS, Tours, France.
Biol Cell. 1988;64(1):45-55. doi: 10.1016/0248-4900(88)90092-5.
Alpha 2-macroglobulin (alpha 2M) is a plasma inhibitor of proteinases, the steric mechanism of which is based on a considerable conformational change. The typical and distinct H-like shape of alpha 2M-chymotrypsin (alpha 2M-chy) complexes seen by electron microscopy led us to an ultrastructural study of the binding of a monoclonal antibody (Mab) specific for this conformation of alpha 2M. The epitope of this Mab is located near the extremities of the 4 arms of the H-like alpha 2M-chy, at a site that is not accessible on the native molecule. The identical binding of the Mab on the 4 arms of the tetrameric molecule demonstrates that these arms are equivalent portions of the 4 monomers. Various types of immune complexes between alpha 2M and IgG are described, and images of individual immune complexes were processed by correspondence analysis. This extracts new information concerning the organization of chymotrypsin-transformed alpha 2M. The molecule appears asymmetrical, presents 2 conformational states (which we describe as relaxed and twisted), and has flexible arms. These intramolecular motions are supposed to be related to IgG binding. The results are discussed in comparison with previously published models of proteinase-transformed alpha 2M.
α2-巨球蛋白（α2M）是一种血浆蛋白酶抑制剂，其空间机制基于显著的构象变化。通过电子显微镜观察到的α2M-胰凝乳蛋白酶（α2M-chy）复合物典型且独特的H样形状，促使我们对针对这种α2M构象的单克隆抗体（Mab）的结合进行超微结构研究。该Mab的表位位于H样α2M-chy的4条臂的末端附近，在天然分子上无法接近的位点。Mab在四聚体分子的4条臂上的相同结合表明，这些臂是4个单体的等效部分。描述了α2M和IgG之间的各种类型的免疫复合物，并通过对应分析对单个免疫复合物的图像进行了处理。这提取了有关胰凝乳蛋白酶转化的α2M组织的新信息。该分子呈现不对称，具有2种构象状态（我们将其描述为松弛和扭曲），并且具有柔性臂。这些分子内运动被认为与IgG结合有关。将结果与先前发表的蛋白酶转化的α2M模型进行了比较讨论。
