Fung Ho Yee Joyce, Mittal Sanraj R, Niesman Ashley B, Jiou Jenny, Shakya Binita, Yoshizawa Takuya, Cansizoglu Ahmet E, Rout Michael P, Chook Yuh Min
Department of Pharmacology, UT Southwestern Medical Center, Dallas, TX, 75039, US.
Department of Biophysics, UT Southwestern Medical Center, Dallas, TX, 75039, US.
Nat Commun. 2025 Mar 16;16(1):2580. doi: 10.1038/s41467-025-57752-3.
Gene expression in response to environmental stimuli is dependent on nuclear localization of key signaling components, which can be tightly regulated by phosphorylation. This is exemplified by the phosphate-sensing transcription factor Pho4, which requires phosphorylation for nuclear export by the yeast exportin Msn5. Here, we present a high resolution cryogenic-electron microscopy structure showing the phosphorylated 35-residue nuclear export signal of Pho4, which binds the concave surface of Msn5 through two Pho4 phospho-serines that align with two Msn5 basic patches. These findings characterize a mechanism of phosphate-specific recognition mediated by a non-classical signal distinct from that for Exportin-1. Furthermore, the discovery that unliganded Msn5 is autoinhibited explains the positive cooperativity of Pho4/Ran-binding and proposes a mechanism for Pho4's release in the cytoplasm. These findings advance our understanding of the diversity of signals that drive nuclear export and how cargo phosphorylation is crucial in regulating nuclear transport and controlling cellular signaling pathways.
响应环境刺激的基因表达取决于关键信号成分的核定位，而核定位可通过磷酸化进行严格调控。以磷酸盐感应转录因子Pho4为例，它需要被磷酸化才能通过酵母核输出蛋白Msn5进行核输出。在此，我们展示了一个高分辨率低温电子显微镜结构，该结构显示了Pho4的35个残基的磷酸化核输出信号，它通过两个与Msn5的两个碱性区域对齐的Pho4磷酸丝氨酸与Msn5的凹面结合。这些发现揭示了一种由不同于Exportin-1的非经典信号介导的磷酸盐特异性识别机制。此外，未结合配体的Msn5被自身抑制这一发现解释了Pho4/Ran结合的正协同性，并提出了Pho4在细胞质中释放的机制。这些发现加深了我们对驱动核输出的信号多样性以及货物磷酸化在调节核运输和控制细胞信号通路中如何至关重要的理解。
