Gonias S L, Figler N L
Department of Pathology, University of Virginia Health Sciences Center, Charlottesville 22908.
J Biol Chem. 1989 Jun 5;264(16):9565-70.
The structure of human alpha 2-macroglobulin (alpha 2M) after reaction with cis-dichlorodiammineplatinum (II) (cis-DDP) was studied by electron microscopy. The cis-DDP stabilized a novel conformation of the native inhibitor resembling a doughnut surrounded by two, three, of four well defined spherules. When only two spherules were present, these structures were usually oriented on opposite sides of the doughnut. The protein region joining a spherule to the central structure did not include sufficient mass to exclude stain and was, therefore, invisible. Other images showed spherules that were partially superimposed on the doughnut. A comparison of many molecules suggested great flexibility of the peripheral spherules relative to the central structure. The cis-DDP prevented complete conformational change when the alpha 2M was reacted with trypsin. The products of this reaction included apparent conformational intermediates. These intermediates most closely resembled either native alpha 2M or the well established "H" structure of alpha 2M-proteinase, depending on the initial conditions used to modify the alpha 2 M with cis-DDP. When cis-DDP-treated alpha 2M was reacted with trypsin, purified by chromatography and subsequently treated with diethyldithiocarbamate, complete conformational change was observed. Based on an analysis of the alpha 2M structural intermediates obtained using the chemical modification procedures described here, a new model of alpha 2M conformational change was developed. We postulate that conformational change initially involves contraction of the peripheral spherules towards the central doughnut. These spherules then unfold and elongate in the perpendicular direction to form the lateral walls of the proteinase transformed alpha 2M H structure.
通过电子显微镜研究了人α2-巨球蛋白（α2M）与顺二氯二氨铂（II）（顺铂）反应后的结构。顺铂稳定了天然抑制剂的一种新构象，该构象类似于一个被两个、三个或四个界限分明的小球包围的甜甜圈。当只有两个小球时，这些结构通常位于甜甜圈的相对两侧。连接小球与中心结构的蛋白质区域没有足够的质量来排斥染色剂，因此是不可见的。其他图像显示小球部分叠加在甜甜圈上。对许多分子的比较表明，相对于中心结构，外围小球具有很大的灵活性。当α2M与胰蛋白酶反应时，顺铂可防止其发生完全的构象变化。该反应的产物包括明显的构象中间体。这些中间体最类似于天然α2M或已确立的α2M-蛋白酶“ H”结构，这取决于用于用顺铂修饰α2M的初始条件。当用顺铂处理的α2M与胰蛋白酶反应、通过色谱法纯化并随后用二乙基二硫代氨基甲酸盐处理时，观察到了完全的构象变化。基于对使用此处描述的化学修饰程序获得的α2M结构中间体的分析，建立了α2M构象变化的新模型。我们推测构象变化最初涉及外围小球向中心甜甜圈的收缩。然后这些小球展开并在垂直方向上伸长，以形成蛋白酶转化的α2M H结构的侧壁。
