White G C, Crawford N, Fischer T H
Center for Thrombosis and Hemostasis, University of North Carolina, Chapel Hill 27599-7035.
Adv Exp Med Biol. 1993;344:187-94. doi: 10.1007/978-1-4615-2994-1_14.
We have presented evidence that rap1b, a 22 kDa low molecular weight GTP binding protein, becomes associated with the cytoskeleton in thrombin-activated platelets. The initial incorporation is very rapid and occurs as fast as we can measure it. Thus, some rap1b is associated with the cytoskeleton as fast as it is formed. The remainder of the rap1b is incorporated more slowly. This biphasic incorporation of rap1b is similar to the incorporation of GPIIb/IIIa into the cytoskeleton, but no interaction between GPIIb/IIIa and rap1b could be demonstrated. Phosphorylation of rap1b by cAMP-dependent protein kinase did not inhibit its association with the cytoskeleton. We conclude that rap1b is one of an increasing number of proteins that associate with the cytoskeleton during cell activation. The function of rap1b in the cytoskeleton is unclear at this time. However, it is possible to speculate on potential roles. There is growing evidence that low molecular weight G proteins participate in the formation of multi-molecular aggregates. For example, p21rac promotes the assembly of a membrane-associated complex composed of NADPH oxidase, p47, and p67 and this complex is important for activation of NADPH oxidase in neutrophils. Similarly, in yeast, BUD1, a homolog of rap1, forms a complex with BUD5 (a homolog of GDI), BEMI, CDC24, and CDC42 (a homolog of G25K). This multi-protein aggregate may be important in cytoskeletal structure in yeast. In platelets, rad1b, which is membrane associated, may promote the assembly of a complex of proteins during cell activation and may localize this complex to the plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
我们已经提供了证据表明，rap1b，一种22 kDa的低分子量GTP结合蛋白，在凝血酶激活的血小板中与细胞骨架相关联。最初的结合非常迅速，快到我们能够测量的程度。因此，一些rap1b一形成就与细胞骨架相关联。其余的rap1b结合得较慢。rap1b的这种双相结合类似于GPIIb/IIIa与细胞骨架的结合，但未证明GPIIb/IIIa与rap1b之间存在相互作用。cAMP依赖性蛋白激酶对rap1b的磷酸化并未抑制其与细胞骨架的结合。我们得出结论，rap1b是细胞激活过程中与细胞骨架相关联的越来越多的蛋白质之一。目前rap1b在细胞骨架中的功能尚不清楚。然而，可以推测其潜在作用。越来越多的证据表明，低分子量G蛋白参与多分子聚集体的形成。例如，p21rac促进由NADPH氧化酶、p47和p67组成的膜相关复合物的组装，并且该复合物对于中性粒细胞中NADPH氧化酶的激活很重要。同样，在酵母中，rap1的同源物BUD1与BUD5（GDI的同源物）、BEM1、CDC24和CDC42（G25K的同源物）形成复合物。这种多蛋白聚集体可能对酵母的细胞骨架结构很重要。在血小板中，与膜相关的rad1b可能在细胞激活过程中促进蛋白质复合物的组装，并可能将该复合物定位到质膜上。（摘要截短至250字）
