Ngoi Peter, Wang Xianxi, Putta Sivasankar, Da Luz Ricardo F, Serrão Vitor Hugo B, Emanuele Michael J, Rubin Seth M
Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA.
Department of Pharmacology and Lineberger Comprehensive Cancer Center. The University of North Carolina, Chapel Hill, NC.
bioRxiv. 2025 Jan 15:2025.01.15.633208. doi: 10.1101/2025.01.15.633208.
Cyclin F, a non-canonical member of the cyclin protein family, plays a critical role in regulating the precise transitions of cell-cycle events. Unlike canonical cyclins, which bind and activate cyclin-dependent kinases (CDKs), Cyclin F functions as a substrate receptor protein within the Skp1-Cullin-F box (SCF) E3 ubiquitin ligase complex, enabling the ubiquitylation of target proteins. The structural features that distinguish Cyclin F as a ligase adaptor and the mechanisms underlying its selective substrate recruitment over Cyclin A, which functions in complex with CDK2 at a similar time in the cell cycle, remain largely unexplored. We utilized single-particle cryo-electron microscopy to elucidate the structure of a Cyclin F-Skp1 complex bound to an E2F1 peptide. The structure and biochemical analysis reveal important differences in the substrate-binding site of Cyclin F compared to Cyclin A. Our findings expand on the canonical cyclin-binding motif (Cy or RxL) and highlight the importance of electrostatics at the E2F1 binding interface, which varies for Cyclin F and Cyclin A. Our results advance our understanding of E2F1 regulation and may inform the development of inhibitors targeting Cyclin F.
细胞周期蛋白F是细胞周期蛋白家族的一个非典型成员，在调节细胞周期事件的精确转换中起关键作用。与结合并激活细胞周期蛋白依赖性激酶（CDK）的典型细胞周期蛋白不同，细胞周期蛋白F在Skp1-Cullin-F盒（SCF）E3泛素连接酶复合物中作为底物受体蛋白发挥作用，使靶蛋白发生泛素化。将细胞周期蛋白F与细胞周期蛋白A区分开来作为连接酶衔接子的结构特征，以及在细胞周期的同一时间与CDK2形成复合物发挥作用的细胞周期蛋白A相比，细胞周期蛋白F选择性招募底物的机制，在很大程度上仍未得到探索。我们利用单颗粒冷冻电子显微镜来阐明与E2F1肽结合的细胞周期蛋白F-Skp1复合物的结构。结构和生化分析揭示了细胞周期蛋白F与细胞周期蛋白A相比，在底物结合位点上存在重要差异。我们的研究结果扩展了典型的细胞周期蛋白结合基序（Cy或RxL），并突出了E2F1结合界面处静电作用的重要性，这在细胞周期蛋白F和细胞周期蛋白A中有所不同。我们的结果推进了我们对E2F1调节的理解，并可能为靶向细胞周期蛋白F的抑制剂的开发提供信息。
