Department of Biology, Institute of Molecular Genetics and Cell Biology, Ulm University, Ulm, Germany.
Comprehensive Cancer Center Ulm, Institute of Experimental Cancer Research, Ulm University, Ulm, Germany.
Life Sci Alliance. 2020 Jul 31;3(9). doi: 10.26508/lsa.202000813. Print 2020 Sep.
Cdc42 organizes cellular polarity and directs the formation of cellular structures in many organisms. By locating Cdc24, the source of active Cdc42, to the growing front of the yeast cell, the scaffold protein Bem1, is instrumental in shaping the cellular gradient of Cdc42. This gradient instructs bud formation, bud growth, or cytokinesis through the actions of a diverse set of effector proteins. To address how Bem1 participates in these transformations, we systematically tracked its protein interactions during one cell cycle to define the ensemble of Bem1 interaction states for each cell cycle stage. Mutants of Bem1 that interact with only a discrete subset of the interaction partners allowed to assign specific functions to different interaction states and identified the determinants for their cellular distributions. The analysis characterizes Bem1 as a cell cycle-specific shuttle that distributes active Cdc42 from its source to its effectors. It further suggests that Bem1 might convert the PAKs Cla4 and Ste20 into their active conformations.
Cdc42 在许多生物体中组织细胞极性并指导细胞结构的形成。通过将活性 Cdc42 的来源 Cdc24 定位到酵母细胞的生长前沿，支架蛋白 Bem1 对于塑造 Cdc42 的细胞梯度至关重要。该梯度通过一组不同的效应蛋白的作用指导芽形成、芽生长或细胞分裂。为了解 Bem1 如何参与这些转变，我们系统地跟踪了其在一个细胞周期中的蛋白质相互作用，以定义每个细胞周期阶段的 Bem1 相互作用状态的集合。与 Bem1 仅相互作用的离散子集的突变体允许将特定功能分配给不同的相互作用状态，并确定了它们在细胞中的分布的决定因素。该分析将 Bem1 描述为一种细胞周期特异性穿梭物，将活性 Cdc42 从其来源分配到其效应物。它进一步表明，Bem1 可能将 PAKs Cla4 和 Ste20 转化为其活性构象。
