Yasuda H, Kamijo M, Ohba Y
Faculty of Pharmaceutical Sciences, Kanazawa University, Ishikawa, Japan.
Yakugaku Zasshi. 1993 Dec;113(12):829-46. doi: 10.1248/yakushi1947.113.12_829.
p34cdc2 kinase plays a key role in the initiation of mitosis. The activity of this kinase requires the binding of a protein, named cyclin, to it. The kinase forms a heterodimer with cyclin. Cyclin A or B is the counterpart of this complex. The differences in the activity between cyclin A/cdc2 kinase and cyclin B/cdc2 kinase have not been cleared. In recent years, the other cdc2-like kinases were identified. One of them was CDK2 (cyclin dependent kinase 2). CDK2 could rescue the defect of the budding yeast CDC28 mutation, which arrested the cells at a point named START, in G1 phase. Then, CDK2 was thought to be worked at G1 through S phase in a cell cycle, but the details on the role of this kinase has not been cleared so far. In this study, we separated the human cyclin A/cdc2 kinase, cyclin B/cdc2 kinase and CDK2, each other by use of column chromatography, and characterized the each kinase. These kinases had the same substrate specificities when the synthesized peptides were tested. They phosphorylated the threonine residue in the sequence -Thr-Pro-Lys-Lys-Ala- but hardly phosphorylated threonine residue the sequence -Thr-Pro-Lys-Ala-Lys-. They had some differences in the substrate-preference when the native proteins were tested. In a cell cycle of human cells, the activity of cdc2 kinase increased at G2/M phase and the activity of CDK2 was high from S through M phase. These data suggested that cdc2 kinase works at the transition from G2 to M phase and that CDK2 works from G1 through G2/M phase. They could phosphorylate different protein-substrates having the common phosphorylated sequence -Thr-Pro-X-Lys-.
p34cdc2激酶在有丝分裂的启动过程中起关键作用。该激酶的活性需要一种名为细胞周期蛋白的蛋白质与之结合。激酶与细胞周期蛋白形成异二聚体。细胞周期蛋白A或B是该复合物的对应物。细胞周期蛋白A/cdc2激酶和细胞周期蛋白B/cdc2激酶之间活性的差异尚未明确。近年来，发现了其他类似cdc2的激酶。其中之一是CDK2（细胞周期蛋白依赖性激酶2）。CDK2可以挽救芽殖酵母CDC28突变的缺陷，该突变使细胞在G1期的一个名为START的点停滞。然后，人们认为CDK2在细胞周期中从G1期到S期起作用，但到目前为止，该激酶作用的细节尚未明确。在本研究中，我们通过柱色谱法将人细胞周期蛋白A/cdc2激酶、细胞周期蛋白B/cdc2激酶和CDK2彼此分离，并对每种激酶进行了表征。当测试合成肽时，这些激酶具有相同的底物特异性。它们使序列-Thr-Pro-Lys-Lys-Ala-中的苏氨酸残基磷酸化，但几乎不使序列-Thr-Pro-Lys-Ala-Lys-中的苏氨酸残基磷酸化。当测试天然蛋白质时，它们在底物偏好上存在一些差异。在人类细胞的细胞周期中，cdc2激酶的活性在G2/M期增加，而CDK2的活性从S期到M期都很高。这些数据表明，cdc2激酶在从G2期到M期的转变中起作用，而CDK2在从G1期到G2/M期起作用。它们可以磷酸化具有共同磷酸化序列-Thr-Pro-X-Lys-的不同蛋白质底物。
