Proteins of the cyclin family have divergent sequences and execute diverse roles within the cell while sharing a common fold: the cyclin box domain. Structural studies of cyclins have played a key role in our characterization and understanding of cellular processes that they control, though to date only ten of the 29 CDK-activating cyclins have been structurally characterized by X-ray crystallography or cryo-electron microscopy with or without their cognate kinases. In this review, we survey the available structures of human cyclins, highlighting their molecular features in the context of their cellular roles. We pay particular attention to how cyclin activity is regulated through fine control of degradation motif recognition and ubiquitination. Finally, we discuss the emergent roles of cyclins independent of their roles as cyclin-dependent protein kinase activators, demonstrating the cyclin box domain to be a versatile and generalized scaffolding domain for protein–protein interactions across the cellular machinery.

细胞周期蛋白家族的蛋白质具有不同的序列，并在细胞内发挥不同的作用，同时共享一个共同的折叠：细胞周期蛋白盒结构域。细胞周期蛋白的结构研究在我们表征和理解它们控制的细胞过程中发挥了关键作用，尽管迄今为止，29 种 CDK 激活细胞周期蛋白中只有 10 种通过 X 射线晶体学或冷冻电子显微镜进行了结构表征，无论有或没有他们的同源激酶。在这篇综述中，我们调查了人类细胞周期蛋白的可用结构，强调了它们在细胞作用中的分子特征。我们特别关注如何通过精细控制降解基序识别和泛素化来调节细胞周期蛋白活性。最后，我们讨论了细胞周期蛋白的新兴作用，与其作为细胞周期蛋白依赖性蛋白激酶激活剂的作用无关，证明细胞周期蛋白盒结构域是跨细胞机器的蛋白质-蛋白质相互作用的通用且通用的支架结构域。