Li Zhan, Kim Hyo Jung, Luoni Laura, Conter Carolina, Masè Nicola, Resentini Francesca, Xie Peiqiao, Astegno Alessandra, Bonza Maria Cristina, Hua Jian
Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853.
Xianghu Laboratory, Hangzhou 311231, Zhejiang, China.
Proc Natl Acad Sci U S A. 2025 Jun 10;122(23):e2504457122. doi: 10.1073/pnas.2504457122. Epub 2025 Jun 2.
Plasma membrane-localized autoinhibited Ca pumps are essential for maintaining basal cytosolic Ca levels for regulating growth processes and environmental responses. These pumps are known to be activated by calmodulins to maintain Ca homeostasis in plants and animals. Here, we demonstrate that the evolutionarily conserved copine protein BON1 is critical for maintaining low cytosolic Ca concentrations by directly regulating two plasma membrane-localized Ca pumps ACA8 and ACA10 in . BON1 interacts with a region within the N-terminal domain of ACA8 and ACA10, preceding the calmodulin binding sites, and stimulates ACA8 activity. This activation can occur without calmodulin binding, indicating that BON1 and calmodulin independently regulate the Ca pump. Loss of BON1 function results in elevated basal cytosolic Ca concentrations, which can be partially rescued by overexpressing hyperactive ACA8 or ACA10. Furthermore, we show that BON1 has one high-affinity Ca binding site in the VWA domain that is critical for activation of ACA8 as well as for BON1 function, suggesting a feedback mechanism for Ca homeostasis at resting concentrations. Our findings suggest that this Ca responsive regulatory mechanism extends beyond , as we show interactions between ACA and BON proteins from algae to flowering plants, pointing to an ancient regulatory mechanism for maintaining low basal cytosolic Ca. Notably, a human plasma membrane-localized autoinhibited Ca pump can also be activated by a human BON protein in a yeast functional assay system, suggesting evolutionary conservation in Ca regulation across species.
质膜定位的自抑制钙泵对于维持基础胞质钙水平以调节生长过程和环境响应至关重要。已知这些泵可被钙调蛋白激活，以维持动植物体内的钙稳态。在此，我们证明进化上保守的copine蛋白BON1通过直接调节拟南芥中的两个质膜定位钙泵ACA8和ACA10，对于维持低胞质钙浓度至关重要。BON1与ACA8和ACA10的N端结构域中位于钙调蛋白结合位点之前的区域相互作用，并刺激ACA8活性。这种激活可以在没有钙调蛋白结合的情况下发生，表明BON1和钙调蛋白独立调节钙泵。BON1功能丧失导致基础胞质钙浓度升高，而过表达高活性的ACA8或ACA10可部分挽救这种情况。此外，我们表明BON1在VWA结构域中有一个高亲和力钙结合位点，这对于ACA8的激活以及BON1的功能至关重要，这表明在静息浓度下钙稳态存在反馈机制。我们的研究结果表明，这种钙响应调节机制不仅限于拟南芥，因为我们展示了从藻类到开花植物的ACA和BON蛋白之间的相互作用，这表明存在一种古老的维持低基础胞质钙的调节机制。值得注意的是，在酵母功能测定系统中，人源质膜定位的自抑制钙泵也可被人源BON蛋白激活，这表明跨物种钙调节具有进化保守性。
