Shteinberg M, Hershko A
Unit of Biochemistry, The B. Rappaport Faculty of Medicine and The Rappaport Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Haifa, 31096, Israel.
Biochem Biophys Res Commun. 1999 Apr 2;257(1):12-8. doi: 10.1006/bbrc.1999.0409.
A large complex, called the cyclosome or anaphase-promoting complex, has specific and regulated protein-ubiquitin ligase activity that targets mitotic regulators (such as cyclin B) for degradation at the end of mitosis. In early embryonic cell cycles the cyclosome is inactive in the interphase, but is subsequently converted by protein kinase Cdk1/cyclin B to an active, phosphorylated form, in a process that includes an initial lag period. This time lag may be important to prevent premature self-inactivation of Cdk1/cyclin B before the end of mitosis. We have previously observed that the phosphorylated form of the cyclosome binds to Suc1, a protein that associates with Cdk1 and with phosphate-containing compounds. We now report that low, physiological concentrations of Suc1 stimulate the activation of the interphase form of the cyclosome by the protein kinase. When Suc1 was present from the beginning of the incubation together with protein kinase Cdk1/cyclin B, activation of the cyclosome took place with the normal lag kinetics. However, when interphase cyclosome was first incubated with protein kinase Cdk1/cyclin B without Suc1, the subsequent addition of Suc1 caused a rapid burst of cyclosome activation and the lag was completely abolished. These findings are consistent with the interpretation that following initial slow phosphorylations of the cyclosome by the protein kinase, Suc1 accelerates multiple phosphorylations that culminate in the full activation of the cyclosome. In support of this interpretation, we find that Suc1 stimulates the phosphorylation of several proteins in the preparation of interphase cyclosome and that the effect of Suc1 on phosphorylation was augmented by prior incubation of interphase cyclosome with protein kinase Cdk1/cyclin B.
一种名为细胞周期体或后期促进复合体的大型复合物，具有特定且受调控的蛋白质泛素连接酶活性，该活性在有丝分裂末期将有丝分裂调节因子（如细胞周期蛋白B）作为靶点进行降解。在早期胚胎细胞周期中，细胞周期体在间期是无活性的，但随后会被蛋白激酶Cdk1/细胞周期蛋白B转化为一种活性的、磷酸化的形式，这一过程包括一个初始延迟期。这段时间延迟对于防止有丝分裂结束前Cdk1/细胞周期蛋白B过早地自我失活可能很重要。我们之前观察到，细胞周期体的磷酸化形式与Suc1结合，Suc1是一种与Cdk1以及含磷化合物相关的蛋白质。我们现在报告，低生理浓度的Suc1会刺激蛋白激酶对间期形式的细胞周期体进行激活。当从孵育开始就将Suc1与蛋白激酶Cdk1/细胞周期蛋白B一起存在时，细胞周期体的激活呈现出正常的延迟动力学。然而，当首先将间期细胞周期体与蛋白激酶Cdk1/细胞周期蛋白B一起孵育而不添加Suc1时，随后添加Suc1会导致细胞周期体激活迅速爆发，延迟完全消除。这些发现与以下解释一致：在蛋白激酶对细胞周期体进行初始缓慢磷酸化之后，Suc1会加速多个磷酸化过程，最终导致细胞周期体完全激活。为支持这一解释，我们发现Suc1会刺激间期细胞周期体制备物中几种蛋白质的磷酸化，并且Suc1对磷酸化的影响会因间期细胞周期体预先与蛋白激酶Cdk1/细胞周期蛋白B孵育而增强。
