Department of Chemistry, University of California, Berkeley, CA 94720;
California Institute for Quantitative Biosciences, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2019 Jul 23;116(30):15013-15022. doi: 10.1073/pnas.1901744116. Epub 2019 Jul 5.
Phosphorylation reactions, driven by competing kinases and phosphatases, are central elements of cellular signal transduction. We reconstituted a native eukaryotic lipid kinase-phosphatase reaction that drives the interconversion of phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol-4,5-phosphate [PI(4,5)P] on membrane surfaces. This system exhibited bistability and formed spatial composition patterns on supported membranes. In smaller confined regions of membrane, rapid diffusion ensures the system remains spatially homogeneous, but the final outcome-a predominantly PI(4)P or PI(4,5)P membrane composition-was governed by the size of the reaction environment. In larger confined regions, interplay between the reactions, diffusion, and confinement created a variety of differentially patterned states, including polarization. Experiments and kinetic modeling reveal how these geometric confinement effects arise from a mechanism based on stochastic fluctuations in the copy number of membrane-bound kinases and phosphatases. The underlying requirements for such behavior are unexpectedly simple and likely to occur in natural biological signaling systems.
磷酸化反应由竞争的激酶和磷酸酶驱动，是细胞信号转导的核心要素。我们重建了一种天然的真核脂质激酶-磷酸酶反应，该反应驱动膜表面上的磷脂酰肌醇-4-磷酸[PI(4)P]和磷脂酰肌醇-4,5-磷酸[PI(4,5)P]的相互转化。该系统表现出双稳态，并在支撑膜上形成空间组成模式。在较小的膜受限区域中，快速扩散可确保系统保持空间均匀，但最终结果——主要是 PI(4)P 或 PI(4,5)P 膜组成——取决于反应环境的大小。在较大的受限区域中，反应、扩散和受限之间的相互作用产生了多种不同的图案状态，包括极化。实验和动力学建模揭示了这些几何受限效应如何源自基于膜结合激酶和磷酸酶拷贝数随机波动的机制。这种行为的潜在要求出人意料地简单，并且可能发生在自然生物信号系统中。
