Bretaudiere J P, Tapon-Bretaudiere J, Stoops J K
University of Texas Health Science Center, Department of Pathology and Laboratory Medicine, Houston 77225.
Proc Natl Acad Sci U S A. 1988 Mar;85(5):1437-41. doi: 10.1073/pnas.85.5.1437.
Well-preserved structures of native and alpha-chymotrypsin-bound alpha 2-macroglobulin were obtained by electron microscopy. Computer processing of these images has shown that the native structure has the shape of a padlock 19 nm long. It is proposed that the native alpha 2-macroglobulin consists of the juxtaposition of two protomers with one protomer shaped like a distorted letter "S" and with the other its reverse image, to form a binding site between the two protomers near the bottom of the complex. On cleavage of the subunits with chymotrypsin, the native structure condenses to 16.7 nm and rearranges so that the interaction between the protomers is near the middle. Two images of the alpha 2-macroglobulin-chymotrypsin conjugate were obtained. We suggest that these images represent the end and side view of this complex. Based on the manner in which the native structure is assembled, we propose that the proteolyzed form of alpha 2-macroglobulin is functionally asymmetric in that both protease binding sites reside on the same half of the complex.
通过电子显微镜获得了天然的以及与α-胰凝乳蛋白酶结合的α2-巨球蛋白的保存完好的结构。对这些图像进行计算机处理后发现，天然结构呈一把长19纳米的挂锁形状。有人提出，天然的α2-巨球蛋白由两个原体并列组成，其中一个原体形状像扭曲的字母“S”，另一个是其镜像，从而在复合物底部附近的两个原体之间形成一个结合位点。用胰凝乳蛋白酶切割亚基后，天然结构收缩至16.7纳米并重新排列，使得原体之间的相互作用靠近中间位置。获得了α2-巨球蛋白-胰凝乳蛋白酶复合物的两张图像。我们认为这些图像代表了该复合物的端面和侧面视图。基于天然结构的组装方式，我们提出α2-巨球蛋白的蛋白水解形式在功能上是不对称的，因为两个蛋白酶结合位点位于复合物的同一半侧。
