Merrick Karl A, Larochelle Stéphane, Zhang Chao, Allen Jasmina J, Shokat Kevan M, Fisher Robert P
Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Mol Cell. 2008 Dec 5;32(5):662-72. doi: 10.1016/j.molcel.2008.10.022.
In metazoans, different cyclin-dependent kinases (CDKs) bind preferred cyclin partners to coordinate cell division. Here, we investigate these preferences in human cells and show that cyclin A assembles with Cdk1 only after complex formation with Cdk2 reaches a plateau during late S and G2 phases. To understand the basis for Cdk2's competitive advantage, despite Cdk1's greater abundance, we dissect their activation pathways by chemical genetics. Cdk1 and Cdk2 are activated by kinetically distinct mechanisms, even though they share the same CDK-activating kinase (CAK), Cdk7. We recapitulate cyclin A's selectivity for Cdk2 in extracts and override it with a yeast CAK that phosphorylates monomeric Cdk1, redirecting Cdk1 into a pathway normally restricted to Cdk2. Conversely, upon Cdk7 inhibition in vivo, cyclin B, which normally binds Cdk1 nearly exclusively, is diverted to Cdk2. Therefore, differential ordering of common activation steps promotes CDK-cyclin specificity, with Cdk7 acting catalytically to enforce fidelity.
在多细胞动物中，不同的细胞周期蛋白依赖性激酶（CDK）与特定的细胞周期蛋白伴侣结合，以协调细胞分裂。在此，我们研究了人类细胞中的这些偏好，并表明细胞周期蛋白A仅在S期晚期和G2期与Cdk2形成的复合物达到稳定状态后，才与Cdk1组装。为了理解尽管Cdk1丰度更高，但Cdk2仍具有竞争优势的基础，我们通过化学遗传学剖析了它们的激活途径。Cdk1和Cdk2通过动力学上不同的机制被激活，尽管它们共享相同的CDK激活激酶（CAK），即Cdk7。我们在提取物中重现了细胞周期蛋白A对Cdk2的选择性，并通过一种能磷酸化单体Cdk1的酵母CAK来改变这种选择性，将Cdk1重定向到通常仅限于Cdk2的途径。相反，在体内抑制Cdk7后，通常几乎只与Cdk1结合的细胞周期蛋白B会转向Cdk2。因此，常见激活步骤的不同顺序促进了CDK-细胞周期蛋白的特异性，Cdk7起催化作用以确保准确性。
