Institute of Technology, University of Tartu, Tartu, Estonia.
EMBO J. 2021 Jan 15;40(2):e105839. doi: 10.15252/embj.2020105839. Epub 2020 Nov 19.
Cyclin-dependent kinases (CDKs), the master regulators of cell division, are activated by different cyclins at different cell cycle stages. In addition to being activators of CDKs, cyclins recognize various linear motifs to target CDK activity to specific proteins. We uncovered a cyclin docking motif, NLxxxL, that contributes to phosphorylation-dependent degradation of the CDK inhibitor Far1 at the G1/S stage in the yeast Saccharomyces cerevisiae. This motif is recognized exclusively by S-phase CDK (S-CDK) Clb5/6-Cdc28 and is considerably more potent than the conventional RxL docking motif. The NLxxxL and RxL motifs were found to overlap in some target proteins, suggesting that cyclin docking motifs can evolve to switch from one to another for fine-tuning of cell cycle events. Using time-lapse fluorescence microscopy, we show how different docking connections temporally control phosphorylation-driven target degradation. This also revealed a differential function of the phosphoadaptor protein Cks1, as Cks1 docking potentiated degron phosphorylation of RxL-containing but not of NLxxxL-containing substrates. The NLxxxL motif was found to govern S-cyclin-specificity in multiple yeast CDK targets including Fin1, Lif1, and Slx4, suggesting its wider importance.
细胞周期蛋白依赖性激酶（CDKs）是细胞分裂的主要调节因子，它们在不同的细胞周期阶段被不同的细胞周期蛋白激活。除了激活 CDK 之外，细胞周期蛋白还识别各种线性基序，将 CDK 活性靶向特定的蛋白质。我们发现了一个细胞周期蛋白 docking 基序 NLxxxL，它有助于在酵母酿酒酵母的 G1/S 期将 CDK 抑制剂 Far1 进行磷酸化依赖性降解。这个基序仅被 S 期 CDK（S-CDK）Clb5/6-Cdc28 识别，并且比传统的 RxL docking 基序要强得多。在一些靶蛋白中发现了 NLxxxL 和 RxL 基序重叠，这表明细胞周期蛋白 docking 基序可以进化为从一个基序切换到另一个基序，以微调细胞周期事件。我们使用延时荧光显微镜，展示了不同的 docking 连接如何在时间上控制磷酸化驱动的靶蛋白降解。这也揭示了磷酸适配器蛋白 Cks1 的不同功能，因为 Cks1 的 docking 增强了含有 RxL 的底物的 degron 磷酸化，但不能增强含有 NLxxxL 的底物的磷酸化。NLxxxL 基序被发现控制了多个酵母 CDK 靶蛋白中的 S 型细胞周期蛋白特异性，包括 Fin1、Lif1 和 Slx4，这表明它具有更广泛的重要性。
