Jeffrey P D, Tong L, Pavletich N P
Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Genes Dev. 2000 Dec 15;14(24):3115-25. doi: 10.1101/gad.851100.
The cyclin-dependent kinases 4 and 6 (Cdk4/6) that drive progression through the G(1) phase of the cell cycle play a central role in the control of cell proliferation, and CDK deregulation is a frequent event in cancer. Cdk4/6 are regulated by the D-type cyclins, which bind to CDKs and activate the kinase, and by the INK4 family of inhibitors. INK4 proteins can bind both monomeric CDK, preventing its association with a cyclin, and also the CDK-cyclin complex, forming an inactive ternary complex. In vivo, binary INK4-Cdk4/6 complexes are more abundant than ternary INK4-Cdk4/6-cyclinD complexes, and it has been suggested that INK4 binding may lead to the eventual dissociation of the cyclin. Here we present the 2.9-A crystal structure of the inactive ternary complex between Cdk6, the INK4 inhibitor p18(INK4c), and a D-type viral cyclin. The structure reveals that p18(INK4c) inhibits the CDK-cyclin complex by distorting the ATP binding site and misaligning catalytic residues. p18(INK4c) also distorts the cyclin-binding site, with the cyclin remaining bound at an interface that is substantially reduced in size. These observations support the model that INK4 binding weakens the cyclin's affinity for the CDK. This structure also provides insights into the specificity of the D-type cyclins for Cdk4/6.
驱动细胞周期G1期进程的细胞周期蛋白依赖性激酶4和6（Cdk4/6）在细胞增殖控制中起核心作用，而CDK失调在癌症中是常见事件。Cdk4/6受D型细胞周期蛋白调节，D型细胞周期蛋白与CDK结合并激活激酶，同时也受INK4抑制剂家族调节。INK4蛋白既能结合单体CDK，阻止其与细胞周期蛋白结合，也能结合CDK-细胞周期蛋白复合物，形成无活性的三元复合物。在体内，二元INK4-Cdk4/6复合物比三元INK4-Cdk4/6-细胞周期蛋白D复合物更丰富，有人认为INK4结合可能导致细胞周期蛋白最终解离。本文展示了Cdk6、INK4抑制剂p18（INK4c）和D型病毒细胞周期蛋白之间无活性三元复合物的2.9埃晶体结构。该结构表明，p18（INK4c）通过扭曲ATP结合位点和使催化残基错位来抑制CDK-细胞周期蛋白复合物。p18（INK4c）还扭曲了细胞周期蛋白结合位点，细胞周期蛋白仍结合在一个尺寸大幅减小的界面上。这些观察结果支持INK4结合会削弱细胞周期蛋白对CDK亲和力的模型。该结构还为D型细胞周期蛋白对Cdk4/6的特异性提供了见解。
